more info on the vehicle its a 4.3L v6 2door
it takes 1-7 seconds to start, and when its in park it runs fine, but when i come to a stop light/sign and sit for too long it starts shaking the whole truck and i have to put it into park until i can go, so far we have replaced the fuel injector, cap and router, spark plugs, both front brake systems, probably more im forgetting, and tonight the starter because i got a load test done on the battery and they told me to get a new starter, (side note : who the frick designed the layout of the engine it is so difficult to work on!!!) and its still not starting right. i havent driven it since we put the starter in but i doubt it would change the way it drives. any and all advice is appreciated

 

1. Any codes?
2. How strong does it pull under hard acceleration and can it get near redline before a shift?
3. When it is running ok in park, step on the brake and tell me if anything changes?
4. You need to do the 10 min fuel pressure leak down test
5. What are your 4 fuel trim numbers?
6. Can you rule out bad gas?

George

 

#3 is the first thing I thought of. Sure sounds like you have a vacuum leak.