Towing and sucking gas like crazy.

[Gibson]

If you're boiling out transmission fluid that's the FIRST thing that needs to be addressed,, somethings wrong big time.
OK, Your truck, being a 2500, is already fairly heavy, then you add a 5K trailer and 1K in the bed,, you're probably already close to the GCWR, the combined weight of everything added together.
The 350 TBI in the 2500s is no powerhouse at all.
It has poor-breathing heads, low compression, and a mild cam.
Wasn't factory HP rating about 175>185, or so.
You're asking a small low HP engine to do a lot of work, especially going up-hill, trying to keep some speed.
All things put together, yeah, it'll suck gas like flushing a toilet.
Hey, the 350s have never been noted as a good mileage engine.

 

[SUBURBAN5]

If you're boiling out transmission fluid that's the FIRST thing that needs to be addressed,, somethings wrong big time.
OK, Your truck, being a 2500, is already fairly heavy, then you add a 5K trailer and 1K in the bed,, you're probably already close to the GCWR, the combined weight of everything added together.
The 350 TBI in the 2500s is no powerhouse at all.
It has poor-breathing heads, low compression, and a mild cam.
Wasn't factory HP rating about 175>185, or so.
You're asking a small low HP engine to do a lot of work, especially going up-hill, trying to keep some speed.
All things put together, yeah, it'll suck gas like flushing a toilet.
Hey, the 350s have never been noted as a good mileage engine.

I agree.

 

[Edmduncan]

Here's my input. 1 make sure you do a tune up if it needs it. Plugs,wires, cap,rotor, fuel filter,air filter, oil, ect. Also maybe rebuild your tbi. 2 put a bigger trans cooler if your always towing, you having a shift kit I believe holds the gears longer which means your burning gas more. Also you having tbi wont be as efficient as the vortecs fyi. 3 depending on your rear end that 350 gonna be working hard to pull. She's gonna be thirsty all the time. However I understand you dont wanna swap it for a different motor. What kind of milage are you trying to get?

Done all the above to the engine. Everything's new on it except the internals. Exhaust, all top works. Tbi rebuilt, etc. 3.73 rear semi floating.
To be honest I think I've done all I can with the exception of a larger trany cooler.
I think a 6ltr ls engine swap is coming in the spring lol.

 

[DerekTheGreat]

If you're boiling out transmission fluid that's the FIRST thing that needs to be addressed,, somethings wrong big time.
OK, Your truck, being a 2500, is already fairly heavy, then you add a 5K trailer and 1K in the bed,, you're probably already close to the GCWR, the combined weight of everything added together.
The 350 TBI in the 2500s is no powerhouse at all.
It has poor-breathing heads, low compression, and a mild cam.
Wasn't factory HP rating about 175>185, or so.
You're asking a small low HP engine to do a lot of work, especially going up-hill, trying to keep some speed.
All things put together, yeah, it'll suck gas like flushing a toilet.
Hey, the 350s have never been noted as a good mileage engine.

I dunno man. It t'ain't horsepower which I look at when thinking about towing, it's torque. These TBI 350's made a decent amount right around 2k Rip'ems. The heads were engineered to flow best right around there. I've done a lot of towing recently, not 6klbs worth but a good 5k or close to it. Unloaded my '89 will do about 17mpg on the highway (details in sig, 3.73 rear gear) and while towing that 5k it was close to 12. On flat stretches I was able to drop it OD but uses 4th for any sort of grade while trying to maintain 50 to 55mph. Not completely sure but I burned about half a tank towing and then the rest of it driving normally and that tank was still about 15mpg. It wasn't a powerhouse, no, but it got the job done just fine. For all the utility and function my TBI truck gives me, I couldn't ask for more.

 

[SUBURBAN5]

Done all the above to the engine. Everything's new on it except the internals. Exhaust, all top works. Tbi rebuilt, etc. 3.73 rear semi floating.
To be honest I think I've done all I can with the exception of a larger trany cooler.
I think a 6ltr ls engine swap is coming in the spring lol.

Looks like a nice truck though

 

[L31MaxExpress]

Done all the above to the engine. Everything's new on it except the internals. Exhaust, all top works. Tbi rebuilt, etc. 3.73 rear semi floating.
To be honest I think I've done all I can with the exception of a larger trany cooler.
I think a 6ltr ls engine swap is coming in the spring lol.

6.0L does not impress me towing. If you really want to tow get a 454 or 8.1 or a Cummins 12 valve.

 

[stutaeng]

I was going to suggest a Vortec swap; either 5.7 or 7.4 should handle that load. If this is a dedicated tow rig, probably go with the 7.4, but if it's a daily driver 5.7 would get better gas mileage (km?) unloaded.However, loaded both are probably equal, around the 8mpg range.

The 6.0 would get about same mileage loaded, and TQ is between the 5.7 and 7.4, but HP is higher at higher rpm by just a bit.

Any swap is going to set you back $2k to $3k on the low range. Maybe less on the 5.7/7.4, maybe more on the 6.0. just something to consider.

 

[Gibson]

3.73 rear semi floating.

OK, now we learn something really important for towing.
If you want to move that much weight you really should have at least 4.10 gearing.
I had assumed that a 2500 would already have 4.10 gears.
Is this a "light duty" 2500 with the 6 lug axles?
Pulling 6K with 3.73s, especially up-hill puts you in the area of pedal-to-the-metal in 2nd gear.

 

[SUBURBAN5]

Looks like a 8lug

 

[Gibson]

Looks like a 8lug

My bad,, you're right, it does look like an 8 lug.
Wouldn't a 2500 8 lug have a GVW of ~8,600?
Anyway, 3.73 is too tall of gearing for a small block GMT400 that has to tow very much weight.