I asked about this 6 months ago and cant seem to find it. But anyway trans shift patter is all over the place. Today rpm 2300 and would not shift, let off the throttle and it would shift. Some times it will skip 2nd and go into third shift back down to 2nd then back to third.
Someone suggested pressure solenoid and something else, I need help with  what something else is. lol

Governor pressure sensor and solenoid. Adjust bands, change fluid, change filter, and I add a bottle of lucas trans fix. Also make sure its the upgraded solenoid. It will be larger than stock and non-magnetic. I get mine from cascadetransmissionparts.com

Yaa! What mopartechnician said! Borg warner solenoid or DNJ extreme duty (more expensive, comes with new mounting plate too). If you have a really hard 3 to 4 shift get that spring too.

I think this should be in the 2nd gen section, if this is the truck in your signature.

The title says r48 so i assume he is talking about an 48re trans in a 3rd gen. That would be my guess

05- 3500 - auto