There are no check engine light or codes stored

 

Ok just got back from dealer they updated pcm with new software which included harsh shift 1-2 program, but it did not seem to change anything on my truck. any other ideas?

 

I have a 99 gmc sierra I had trans replaced almost a yr ago and has been fine until last week and it started no dropping down to first and acts like it's in tow haul mode and if you mash tow haul nothing happens but if you stop and cut trk off and crank it back few mins later it starts off like it should any ideas