In Dare Need, 95 K1500 Speed Problem??

[dalepre]

Hello Everyone,
I have spent app 6 months trying to figure out the issue with my truck,I have spent hours searching.
1995 Chevy K1500, Extended Cab, 350 with TBI, 4L60E trans,234,000 miles, standard bed,

I have owned this truck since new, I have always changed the oil every 3000 and run Mobil One oil, the only thing till now that has been replaced under the hood before was:
1 Water Pump
1 Raditator
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, 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.

This truck has never even been in the dirt.

The only towing has been my 19 foot Skeeter Bass boat(reason for the tranny replacement)

When this problem raised it's ugly head, it did it in just 2or 3 miles.

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 exhust manifold (saw a hair line crack whiledoing plugs)
New MAP Sensor
New Thermostat(just for the heck of it) have had no issuesat 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 differentGM dealerships, 4 other lifelong mechs 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 a instant, no missing on any cyls, no backfire,no sputtering, baby smooth idle always, oil pressure hangs around 50-60 psi atall times, lowest you might see is 45. Water temp just were it should be rather solid on 210.
You can start it upand take off, also engine hot or cold has no bearing at all.
If you pull out on the hwy and apply the gas VERY lightlyand allow the truck to build up its speed very slow you can go down the interstate with cruiseon at 80-90 and never know there is a problem.
Now, if you go WOTwhen you are running 55, in O/D, tach at app 1500 rpm, the tach jumps up to3400-3500 RPM in a instant, like a rocket, no missing, sputtering nothing atall, but the truck speedo stays on 55 and you go no faster, you can stay at WOT(Wide Open Throttle) for 5 10 seconds and the tach 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 be 20-30MPH 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 her on the last mile or so the the above 10 and she hit 100 and running as smooth as a babys bottom.
The tranny never slips, whines, nothing at all to notice. I also change my tranny fluid and filter every 50,000 like clock work.

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, no change in my truck at all, Put the TBI off my truck on the Suburban and it ran justlike it did with its TBI installed, so no problem there.
Thanks in advance forany and all help.

Beaten,
Dale

[777stickman]

Welcome to AF. I'm not a tranny guy, but, after reading your post several times I'm inclined to suspect it's just that. Think about it, easy gas and it goes, hard gas and it doesn't. The power under heavy gas is just not getting to the rear wheels. Hopefully some tranny guys will step in with some ideas.

[Schurkey]

Fuel pressure with the throttle stamped to the carpet and the tach at 3500 RPM?