Lots of new parts but runs horrible

[CJA755]

I have a 1997 GMC K1500 that I have put a new fuel pump, transmission, and engine with a bunch of other stuff to go with the engine so I could get the warranty and still have some old problems and now a new one. The old problem is the truck doesnt like to start when its hot, with the old motor and with the new one I put in, it starts fine when cold and runs fine, but once I stop to get gas and get back in to start the truck it drags really bad and slowly comes to life or starts so hard the whole thing shakes, I do have a new starter too.

The new problem I have is despite all of the new stuff in the truck and it running good for maybe a month of consistent driving it started having hiccups(best way I can think to describe the issue) but going down the highway at 65mph the rpms would start bouncing up and down only a couple hundred at a time as if I was repeatedly lightly tapping the gas pedal despite cruise control being on or even if it was off and just maintained the speed manually. The hiccups turned really hard lurching and sputtering after about a week when I went to leave for and got on the road for barely a quarter mile before the rpms went crazy and the truck sputtered like it was out of gas and lost power for a sec before turning back on by itself and continuing drive and the lurching started as well like the truck didnt know what gear it wanted to be in. As if I was shifting it back and forth between 2nd and 3rd while trying to accelerate at the same time. I have so much money and emotional value in this truck and dont have money for a newer one.

 

[evilunclegrimace]

Hook up a scanner and see what the data stream is showing. With out any information from the trucks data stream any answers that you get will be guesses.

 

[WICruiser-97]

What parts did you transfer over from the old engine to the new?

For the starting issue look closely at the battery calbe that run to the starter and engine. A lot of times they are corroded inside the outer covering and provide a lot of resistance.

 

[RLC2020]

as stated above, battery ground cable is a must to check and clean up. I'd also look at the fuel filter/fuel tank. Clogged filter, bad pump, bad ground at the pump, or worse a rusty tank with bad gas in it can cause your hiccups.

 

[CJA755]

What parts did you transfer over from the old engine to the new?

For the starting issue look closely at the battery calbe that run to the starter and engine. A lot of times they are corroded inside the outer covering and provide a lot of resistance.

I didnt transfer any old parts from the engine. I bought all new stuff when i got the new motor to put in except wiring, thats the only old stuff

 

[CJA755]

as stated above, battery ground cable is a must to check and clean up. I'd also look at the fuel filter/fuel tank. Clogged filter, bad pump, bad ground at the pump, or worse a rusty tank with bad gas in it can cause your hiccups.

I have a newish fuel pump, maybe 3 years old. But the truck did sit for awhile after the transmission went out until i got money to fix it, then motor went out a week after getting the new transmission and sat for about a year until i got the money for a new motor. But i ran through maybe 6 tanks of gas without any issue until recently

 

[RLC2020]

could be a filter then, but if all else fails it's not too terrible to drop the tank and check out what's going on in there. Not a fun job, but doable.

 

[evilunclegrimace]

could be a filter then, but if all else fails it's not too terrible to drop the tank and check out what's going on in there. Not a fun job, but doable.

How about running a fuel pressure test first?