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I do not know if the 4L80 TCM stores codes that are no longer active, most of the later stuff does, in fact I did not think the 4L80 got a dedicated TCM until the mid 2000s (2005?) so the HMMWV may actually be using a modified PCM (powertrain control module) as that is what controlled the...

It is normal for the transmission to not go into torque converter lock until the transmission comes up to temperature. this will seem like it is not shifting into high but much different than being stuck in 2nd. If it is stuck in limp mode it will not shift at all when in drive, it will start...

Have you checked to see if there are codes from the TCM? You need to learn how to do it so if there are not any stored codes you can get them on the fly when your transmission is not working properly, that will be the best way to figure out where your problem is. otherwise you are just peeing...

You have a 4L80 You power cycle the TCM by disconnecting the batteries, but do not do that until you read how to get the codes off of the TCM, this should help. You do not want to erase the codes before you read them.

Do you have a 700R4 transmission? if not you do not have a TV cable. If you have a 4L80 it sometimes helps to power cycle the TCM but see if you have any codes first.