I have a 1996 12 valve with the 4.10 axle ratio and auto transmission 4x4. The other day I was pulling a custom b-que pit that maybe weighed 5000 lbs and I could not accelrate past 67 mph and around 2300 RPM's. I would floor it and everything and it would stay at that same speed and RPM's . Is this normal for the 4.10 and auto trans? I'm pretty new to this so I thought I would ask. Also when I pull my boat I can get to about 2500 RPM's but not to the rev limit of 2700. The fuel filter only has about 700 miles on it so it should be good and while running with no load I have no problems with acceleration.

 

Perhaps your IP is running out of fuel pressure as could happen if your overflow valve is worn out (estimated life 75,000 miles). Overflow valve is in the banjo bolt at the top front of the IP.

Do a search here for overflow valve and you get a day's worth of reading.

Welcome to this forum. Fill in your signature (how many miles on your truck?) and keep us posted.

 

Rare1 gives good advice.
The overflow valve is the single part that wears out most on a 12 valve and is always a good place to start for your simptoms. 5 minute, one wrench job to replace it.

You won't find a better price than here

Precision Diesel Injection and Turbo Inc.
Marty Tompkins
888-734-7349
$35 + $7 shipping and handling.

Object at lower left is the oil fill cap

 

Might want to check your throttle cable. The cable, over time, will get a little longer than it needs to be the truck will be fairly sick with no WOT. I think there is a saftey recall for the cable.

 

I personally feel that its probably just the stock governor springs holding you back. They defuel at like 2400rpm's, and mine was the same way before the GSK. Get a 3k GSK, aqnd you will be VERY happy.

Eric