Sometimes it seems like my truck feels a little sluggish until i get on it a bit and get the rpm's up. After that it feels like a different truck when I go back to driving normally. I don't do it too much, just drop it down a gear on the interstate for a second. Almost seems like it's clearing some kind of clog issue or something. I guess it could be in my head? '99 4.6 v8 very well maintained.

 

Your forgetting the PCM shifts table history over time, based on how it is being driven.
My truck comes off a towing session then feels more peppy unloaded, but fades off after a few drive cycles normal unloaded driving, as well as temp changes make a difference..
I notice consistantly more pep in the 45 to 65° ambient temp ramge.
You got this little monkey in the box calling a lot of the running shots.
It's called adaptive learning.

 

Is there any way to reset the PCM safely? Make it re-learn everything?

 

I noticed the same thing. I compare it to my old 1979 Cutlass Supreme 2 dr. Had a 305 4 bbl.. If i gunned it out of the hole, it fell on its face. Feather the throttle till some speed builds up, then punch it, feel the secondaries open up. If i give the truck easy throttle, then it responds better...

I dunno...