Problen with accelaration, but engine revs up fine

  • 234,000 MILES
I have spent app 6 months trying to figure out the issue with my truck.
Chevy K1500, Extended Cab, 350 with TBI, 4L60E Trans, 234,000 miles, standard bed,

I have owned this truck since new, the only parts that have been replaced under the hood are:
1 Water Pump
1 Radiator
3 Sets of OEM original plugs
3 Sets of OEM wires
3 Dist. Caps and rotor
1 starter
3 Throttle Position Sensors
That's It!

Transmission was replaced app. 70k ago with a new GM crate unit, system was not just flushed, I replaced all lines, coolers, and everything there was.

Only other repair was to replace the speed sensor on the transfer case app. 50k ago.

Only other service has been brakes, rotors, etc.

Now, items that I have replaced trying to correct:

NEW GM Complete Dist. Unit
New Plugs, wires.
New OEM bolt on GM Cat. Converter
New OEM O2 Sensor
New right hand exhaust manifold (saw a hair line crack while doing plugs)
New MAP Sensor
New Thermostat (just for the heck of it) have had no issues at all with engine temps at all
New Coil
New AC Delco Vacuum Valve
New Vapor Canister Purge Solenoid

All of these items have less than 10 miles on them.
3 different GM dealerships, 4 other lifelong mechanics and a few others along the way.

The truck starts like it did the first day, just tap the switch and she roars to life in an instant, no missing on any cylinders, no back fire, no sputtering, baby smooth idle always, oil pressure hangs around 50-60 psi at all times, lowest you might see is 45. Water temp just where it should be rather solid on 210.
You can start it up and take off, also engine hot or cold has no bearing at all.
If you pull out on the hwy and apply the gas VERY lightly and allow the truck to build up its speed very slow you can go down the interstate with cruise on at 80-90 and never know there is a problem.
Now, if you go WOT (Wide Open Throttle) when you are running 55, in O/D, tach at app 1500 rpm, the tach jumps up to3400-3500 RPM in an instant, like a rocket, no missing, sputtering nothing at all, but the truck speedo stays on 55 and you go no faster, you can stay at WOT for 5 10 seconds and the teach stays wound out, but no go. Same action if you go from a dead stop taking off and go WOT, tach goes to above and speed may be20-30MPH and no increase. Back of the pedal and let her get up to speed slowly and it will twist the speedo till the limiter cuts her off. I had it hitting 100 and running as smooth as a baby’s bottom.
The tranny never slips, whines, nothing at all to notice. I also change my tranny fluid and filter every 50,000 like clockwork.

Also pulled the TBI unit off of my 1995 Suburban, TBI has same numbers stamped on it has my truck, exact same running gear, 90k on it, made no change in my truck at all, Put the TBI off my truck on the Suburban and it ran just like it did with its TBI installed.
Thanks in advance for any and all help.

Do you
have the same problem?
Sunday, May 19th, 2013 AT 11:05 AM

1 Reply

Has fuel pressure and delivery rate been checked?
Was this
Sunday, May 19th, 2013 AT 1:59 PM

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