I did a search and I couldn't find anything... So

I last drove my truck a couple of weeks ago with no transmissions issues at all. It has been parked (level ground) I went to move it and it has no reverse at all

And when I put it in Drive it Clunks hard and hardly moves forward. Also the sq indacator thing over P R N D 3 2 1 blinks when in R D 3 2 1....Filter and oil are both good.

I let the truck sit for about 15 mins and now it's all ok.. Should I be concerned??

2002 8.1 witk a stock allison 94.xxx mi

Sounds like could be the NSBU switch-- common problem as they are exposed to the rain and snow. :D

I replaced the NSBU switch about a year ago with the good one (not saying it isn't it again). I'm in So Cal also no rain or snow just quakes and fires..Thank you

Anyone?

The 2001 and '02 had 25 psi lube pressure that allowed the air bubble from a drained down torque converter to burp into the pump inlet causing loss of prime. This can set a code and limit operation. The '03 and later had 40 psi lube pressure and more robust software. It is likely the cause, if you haven't had updates.

If it happens again, throw it in park and rev up the engine for about 30 seconds. Shut off and restart. Should be good to go.

Thank you!!