8.1L/4L85E torque converter?
 

From what I understand, the OEM TC doesn't lock up 100%. Whether it's the friction material or the GM torque management geniuses I don't know. But wondering if there's an aftermarket converter that will lock up 100%. I'm starting to look into either a switch that I can lock it up manually, or just reprogram the ECU and see if it will lock up in 3rd and/or lower the lock up speed. Right now it doesn't lock up until just over 50mph. In Tow/Haul it will lock up in 3rd. I need to lower the upshift speeds for Tow/Haul also. Every little bit to help gas mileage these days.

Michael,

Have you tried the Diablo Predator tuner yet? It gets a majority percentage of the torque (lock-up) back for you. (You will have to check with them for the exact number.) I was told the factory programming only limits you in 1st gear, but I could be wrong. It is/was a noticeable difference on my former truck.

Also check with bully dog. This gas downloader may be the ticket.

40510 - GM Gas Trucks and SUVs '99 - '08 Buy Now
The Triple Dog Gas Downloader is a programmer/tuner that downloads horsepower and performance enhancing programs into three different vehicle makes of pickup trucks and the Mustang in one SKU (stock keeping unit). The downloader offers two different Engine Tunes above stock to accomodate various driving conditions; read below for recommended use. Engine Tuning Programs

The engine tuning options below describe what tunes are available through the Triple Dog and their recommended use.



Stock: Choosing the Stock engine tune will result in no change to engine horsepower output. All other downloader features can still be accessed if the Stock engine tune is choosen.
Regular: This engine tune is recommended for use with 85 or 87 octane gasoline. For maximum effectiveness end users should increase shift firmness and shift points. This tune can be used for everyday driving and towing. Dynamometer testing results have shown a 10-12hp increase in rear wheel horsepower.
Premium: This engine tune is recommended for use with 91 or 93 octane gasoline. It is recommended that shift firmness and shift points be raised with this engine tune. This tune can be used for everyday driving, towing and racing. Dynamometer testing results have shown up to 25 horsepower and 24 lbs. ft. torque increase, on the premium tune, to the rear wheels.

All the handheld tuners do is reduce or eliminate Torque Management. That's GM's method of retarding timing in the ECU so the transmission doesn't die a premature death. I don't mind TM in this truck, it's probably saved me at least one right rear tire. :D Of course the handhelds can alter shift points and shift pressure too, but none of that relates to the TC itself. I haven't touched the ECU in this truck but I always get custom tunes; I have a spare that needs to go out for my headers so I'll have them work whatever they can in that area.

The torque converter itself actually has a disc and friction material...like a disc brake. When a TC "locks up", it's supposed to clamp down and minimize hydrodynamic power loss. The TC in these powertrain combos doesn't actually lock up 100%. I haven't read up on it in a while but I think it was actually due to the friction material.