The reason the allison TCM wont lock up is this:
Whenever turbine vs. input speed 'delta' (sorry im not just trying to sound smart or sophisticated by saying that, honestly) is greater than ~650-700rpm, the TCM will inhibit lockup under ALL conditions. Also, if turbine vs. input speed delta is LESS THAN 0rpm (that is, the converter turbine is spinning faster than the engine, like if you are coasting down a hill at less than ~50mph in non-tow/haul mode), converter lockup is also inhibited.
The only reason for this is to prevent driveline shock (and potential damage to trans hard parts, and driveline components) under high speed differences, when the converter is slipping (multiplying torque) a lot before it couples. Note I said "COUPLES". Coupling is not the same thing as lockup.
The TCM inhibits lockup at high slip rpm's to allow the converter to "catch up" with itself and couple a bit so the slip speed is closer to zero...the closer the slip speed is to 0rpm, the less harsh the lockup will be (when it occurs/when its commanded by the TCM), because you arent trying to force engine speed/wheel speed differences to suddenly match. Like if you're going 40mph in a manual trans truck, clutch in, put it in 1st gear, then let the clutch out. Obviously not going to be very smooth.
So basically.
Allison did this (put this programming in the TCM) only for "driveability" (so customers wouldnt complain about harsh lockup), and to prevent driveline shock, which could result in lots of warranty claims/breakage.
The TCM is infinitely programmable. To say "its programmed so it wont lockup from a stop, BUT that also means we're stuck with failure to lockup at high speeds too" is incorrect. Allison can make it do whatever they want with the software. This is a 21st century designed/programmed computer. You can have your cake AND eat it.
So when you have big power and a looser converter, its easier to "blow through" the converter during a hard boosted launch, and therefore it takes a while for the converter to "catch up" (couple) enough to where slip speed drops below ~650rpm (and therefore crossing the threshold where the TCM will allow lockup to occur again).
Ive been saying this/explaining this over and over again for years...how come people are still asking why the TCM doesnt lockup at higher power levels etc...?
You have two options to fix this, and get the converter to lockup under big power:
A) custom TCM programming. If you can eliminate that inhibitor in the TCM calibration, you'll be all set. EFILive doesnt have access to this parameter [yet]. All of the TCM tables currently available for us WILL NOT FIX/HELP THIS ISSUE. Ive seen people say that they've made some gee-whiz magical TCM tune with EFILive that makes the converter lockup properly/predictably under all conditions but they are all full of crap.
B) aftermarket lockup controller. Im not saying this to try to sell my widget. Believe me I would love it if we had access to it in the software. It would be 10x easier and cleaner to make it work PROPERLY within the TCM and not a harness "fooler" box. But I dont think its going to happen because Ive been asking for probably close to 5 years and no one has had an answer
Ben
