i have a big problem with my truck. i have started the tune up proccess with it. i have owned it for a while but wasnt on my a+ list since i had another car (acura integra) i never payed any attention to it until recently. i owned it for 1 1/2 years now and the first year i never serviced anything. it is equipped with the 4.3 vortec v6. i have changed the fuel filter, plugs, rotor, water pump, and exhaust (gutted cat and new piping w/delta flow exhaust). i have also added a custom built air intake i made myself. my check engine light is usually on due to my tranny valve sticking, so i dont pay attention to it. well i ran a code check today at autozone just to make sure because the truck runs like doodoo. well what do you know 2 sensors reading the truck runs lean. what do i do ? i took it to a shop to check my fuel pressure and everything checks out just fine. but when i get in my truck start it and take off it almost dies from a severe bog. for a truck that use to smoke em leaving the light i cant get it to bark at all. just bogs. any suggestions? tranny has been service, new (high mileage) oil and filter, everything is almost new except wires and cap. i am changing the cap today. maybee some injector cleaner today too but i dont think thats gonna do the trick. please help!!!!!!!!!!

Maybe the fuel pressure regulator? Not sure about the V6 but it was quite a pain changing on my 5.0. Still very doable though. Have you got a service manual to consult?

It could also be a slow reading airlow sensor or a leak in the intake system anywhere from the sensor to the intake manifold maybe could cause it to run lean.