I used to have an 89 ECLB 7.4 with 4:10
It pulled a gooseneck dual axle flatbed with two ford F150s on it over Snoqualmie pass and managed about 40 mph doing it.
It didnt like it, but it did it
I also met every gas station employee on the way.
I'm a bigger fan of the GMT400 platform Than The 800.
The 800 will do the job for sure but they shed little plastic parts and have in my opinion way to many relays and sensors that are starting to be aftermarket only.
The 400 has the same problem but they are much easier to repair and I think we end up dealing with less future part issues.
If you have the time, scour the internet for a Gmt400 that is aready set up for trailer towing.
But the best way to find a deal is to get to know the whole Gmt400 system
So many of these trucks have been parked and sell dirt ass cheap because of really simple things.
I paid 250 bucks for the 89, It wouldnt idle and ran like crap at cold start.
TBI base gasket.
I paid 1500 bucks for my current K2500.
No start, slow start, crazy electrical.
All of the grounds were loose or missing.
That was about 130,000 miles ago.
If I had 4 to 6 k?
I would take my time untill I found that peach.
Remember, you aint kneecapping the dumb, you are saving a truck from the crusher!