Issues with 8.1 Vortex with Allison Transmission

first Ive heard of one getting better than 10 mpg with 4.10 gears.
had an 03 with 4.10s would get 8.5 pulling Our old 5vr and 9.9 empty with a tail wind. was a beast and would pass anything but a gas station.replaced a ball joint and fuel pump, also worn out gas cap.

had to replace both fuel pumps one year apart while on vacation…. truck had about 80000-90000 miles on it …. first time on i-80/90 in chicago rush hour traffic , next time doing 465 bypass around indy in traffic

I have a 2001 2500HD 8.1 Allison and love it! Only drawback is getting places to fuel it up. Getting an average mileage of 11-13 towing the 5th wheel and 16-17 without. Plus it's paid for and only has 91k miles.

We looked at one, but it was the wrong color. (Also wrong fuel.)

mbrower wrote:

nremtp143 wrote:
I have a 2001 and love it. Not enough power to pull my big 5er on the interstates, but a very good dependable truck. Replaced a throttle position sensor(pedal), O2 sensor and a Neutral Start Backup Switch like has already been stated. Good truck. 143,000 miles

You must have one heavy fifth wheel. I tow my Montego bay quad slide fairly easy except steep mountain grades and even then, its acceptable. I don't tow faster than 65/70 mph though. I like the way it tows but wished it got better mpg. The only thing I have done to mine engine/transmission wise is put in a new battery. I think a diesel would be more efficient but mine is paid for and in excellent condition so I will live with the poor mileage a little longer. IMHO it is the best gas towing machine available.

Slow down to 60-65 and your mileage will improve quite a bit. I picked up 1-1.5 mpg in my Duramax, on average.

Lyle

The early Allisons had some issues if you began to do engine mods increasing HP & torque, and the transfer case pump rub issue has a fix. There is compatibility issues with the trans fluid and seals, TES-295 being the better fluid. As said, go to GM truck forums; they will highlight any problems and solutions.

nremtp143 wrote:
I have a 2001 and love it. Not enough power to pull my big 5er on the interstates, but a very good dependable truck. Replaced a throttle position sensor(pedal), O2 sensor and a Neutral Start Backup Switch like has already been stated. Good truck. 143,000 miles

You must have one heavy fifth wheel. I tow my Montego bay quad slide fairly easy except steep mountain grades and even then, its acceptable. I don't tow faster than 65/70 mph though. I like the way it tows but wished it got better mpg. The only thing I have done to mine engine/transmission wise is put in a new battery. I think a diesel would be more efficient but mine is paid for and in excellent condition so I will live with the poor mileage a little longer. IMHO it is the best gas towing machine available.

155k on mine and it's never missed a beat.
Love it.

I have a 2001 and love it. Not enough power to pull my big 5er on the interstates, but a very good dependable truck. Replaced a throttle position sensor(pedal), O2 sensor and a Neutral Start Backup Switch like has already been stated. Good truck. 143,000 miles

Transfer case has an engineering defect where an internal ring will vibrate against the housing eventually causing a small pin hole in the housing. For more than you'd want to know on this see this:

Pump Rub


Also brake/transmission/oil cooler lines rusting out is a known issue too. But that's not confined to the Chevy/GMC 8.1 trucks but rather many from 2000-2009.