A few issues...

• Just a quick history on the vehicle: I bought it about 6 years ago from my grandfather's estate when he past away. I learned how to drive on the thing so there is some setimental value in it... When he was alive he had a 26ft Camper Trailer and when you were towing it, you'd forget it was there. Now if I so much as tow an empy car trailer I have a problem accelerating onto the freeway, once at speed it seems to take an awful lot of gas to maintain speed and forget about trying to pass someone...
  
• I know part of these issues are from neglect (I don't drive the vehicle very often due the horrible gas milage ~ 6 mpg +- 1). I did drive it to Colorado approx 3000 miles round trip and had the tranny loose the "sun sprocket" or something along those lines leaving me only drive 2 & 3 as well as park... Well manually shifting while very tired will let you slip and put the shift lever in park while getting on the freeway... This will make park no longer work for any of you guys out there who want to try it... So I replaced the transmission about 10,000 miles ago with a rebuild from the chevy dealership...

1. Almost no power, I feel like I'm driving that good old Ford Courier my dad had... When towing my boat (2260 lbs) I can barely get up hills without it dropping all the way down to drive 2. (Nothing like going 60 mph then having the truck drop to drive 2. Talk about some rpms...)
2. My entire dash assembly (lights and guages) all flicker up and down when the turn signals are on... The volt guage goes all the way down to 8 and up to almost 18... (put a voltmeter on the battery, cig lighter, and ign wire harness and the voltage doesn't change.) I'm assuming its a ground issue, but have no clue where the ground wire is / bolts to...
   
3. My suspension seems way to week, about 300 lbs and its squatting to the overloads with my mud flaps hitting the ground... Any suggestions or is suppose do that?
   
4. Seems to not want to start when cold, will take 2-3 tries... Think its fuel related because if I just turn the ignition on and off 4-5 times it starts on the first try.
5. I think the power brakes are going out, It just seems like it isn't helping as much as it should, and whenever I release the brake pedle (@ idle) the engine idles up...

1. Replaced Cat (Vehicle had problems starting, thought this was related, wasn't but did help the power issue some...)
   
2. Replaced Muffler (old one rusted out...)
   
3. Replaced Transmission (rebuld)
4. Standard Tune-Up (plugs, wires, cap, rotar)
5. Replaced starter (engaged but wouldn't dissengage, drove about 2700 miles this way [:D] before it gave up...)
   
6. Replaced battering wiring (was old and starter wasn't starting too well, read above)
   
7. Replaced battery (1800 cca)
8. Replaced Alternator (bearing went out in old one...)
   
9. Replaced fuel pump (that gave me my fuel guage back too )
10. Replaced Master Cylinder (peddle dropped to floor and wouldn't return, seal inside MC had gone bad...)
    
11. Replaced Calipers (leaking)
    
12. Replaced Slave Cylinders (leaking)

quote:

ORIGINAL: northey87

Do you remember what the oil presure was when it was running well? The reason I ask is because low oil presure can sometimes be an indication that it is time for a rebuild. 

quote:

ORIGINAL: 06chevy5.3

try doing a decarb on it and see if that helps any, they usually sell it at your local auto parts store. you warm the car up and poor it down the throttle body a little bit at a time and you will see all that crap come out the tail pipe, if you have never done it befor it should put on a hell of a smoke show,