Cool! I'm happy to learn that if you select 2nd, that's what it starts out in. I'd have designed it that way myself. But, you're saying the GMC upshifts when it's in "trailer mode"? That's an interesting way to modify it too and it also makes sense. You'd want a 1-2 upshift when towing, I think.
About this sluggishness, I don't know. I wonder if the torque converter locks up quickly? It has to unlock to allow the vehicle to remain stationary with the engine running, but maybe once it's moving, it locks.
As another observation, I've never seen a lock indication when accelerating in drive with the OD on until I reach 4th gear, no matter how softly I try to accelerate or stabilize the speed early. And, we talked about this in another thread and I think it should lock in third if the OD is off and in 2nd if the transmission is set to run there and so on.
- Jack
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