Please read. Transmission help.

[98GMCz71]

I have a 98 GMC Z71, has ran great ever since I had it.... Up until here about 1-2 weeks ago.
Nothings been replaced transmission or motor wise besides a power steering pump, but here a few days ago I noticed my two wheel hi light would go off while just driving on the road (yes I have push button 4 wheel drive, not by choice ) and then my transmission will kind of bump harder whenever it shifts out of 1st. If I cut my truck off and let it cool for about 5-10 minutes and then start it back up the 2-HI light is back on and my transmission is smooth as ever.
Anyone have any suggestions on things to replace or clean? I'm refilling my transmission fluid in the next day or so. Thanks in advance guys!

[Itsmehuey]

Check you ECM and Tcm for codes first and go from there. The harsh shift could be due to high line pressure commanded by the transmission control module