2005 3/4 ton Avalanche with 8.1. Same story here and glad I got one of the last ones around. I get offers on my truck all the time from diesel owners looking to get back to gas. 14-10 mpg no matter what it does and a quart between 5K oil changes. If they did offer the Allison with this truck it would have been a much bigger seller I bet.

Pulls my 35 no problem and a comfy daily driver.

2008 was the last year you could order an 8.1L and allison in a GM truck.

Just a nice big quiet engine truck with great pulling power and years of trouble free operation!

Everybody who owns one and uses it for towing and such loves them, except for the mileage sometimes.

Sometimes 8.1L owners/boaters don't realize how much Raylar works with 8.1L truck owners on power and torque upgrades. The Raylar BCK102 kit with our aluminum heads and our BP202 camshaft and a good ECM reflash will make a torque monster out of an 8.1L truck and in most cases with good exhaust upgrades like our stainless long tube headers will take the horsepower up around 500HP and the cruising and towing mileage actually improves. This engine stock makes about 320-340HP and about 450 lb/ft of torque and after mods like this customers see 500HP and 600lb/ft. of torque!
Customers we have worked with over the years on such upgrades always say they don't recognize their own truck once they have made these type of improvements. Lets face it a stock engine making only 320 hp from 496 cubic inches is pretty pathetic!

Best Regards,
Ray @ Raylar

Mine is a 2001 3500 8.1 4x4. I love the truck. It has 107,000 miles. Because it sits alot, the brake lines just had to be redone and I recently did the exhaust. I put a cold air intake on it, re chipped it and gibson exhaust and it runs like a champ. As all have stated, it is thirsty but it rides and pulls like nothing else. Good luck with yours!

Does that 500HP/600TQ kit come with a built transmission? I know that you can limp the allison transmission if you put that much power to it. 450 HP is about the max the allison transmission will handle.

Nope.

Bummer they stopped making the 8.1, seems like something that does not blow-up is what GM needs to keep, not this junk 6.0Ltr, every time I use my buddy truck I come back and say how much noise can a motor make before it reaches temp. Piston slap forever, just a plug.

Getting rid of this motor in the HD trucks was a stupid move on GM's part. I'd love to buy a new truck but I don't want a diesel so I've maintained my 2001.[/QUOTE]

We have many customers with stock Allisons behind the 450-500HP Raylar kit upgraded 8.1L engine trucks with no mods or upgrades to the Allisons other than programming changes made in the ECM's and I have heard of a few who done Allison upgrades but I believe a few of those were done becuase they, drive them like they stole them, race the trucks or use them in tractor pulls and such. I am not an Allison expert by any measure but I think its a pretty strong transmission stock unless it like any transmissions has mechanical problems or issues to begin with.

Best Regards,
Ray @ Raylar

Did you (Kurt) have problems with a 4L80e? I have one behind a carbed 454. I just use it to tow but, I'm happy so far. I bet i don't get 6 mpg. lol

yes, blew it up, old haul truck busted forward drum and destroyed trans. Had to buy differant case and rebuild. Bummer. After rebuild it was OK. but for how long??

Plus it always lugged when towing, needed a another gear i always stated. LIKE A ALLISON