What's been happening lately is: If i'm cruising at around 60mph and put it to the floor, it downshifts into 2nd and won't upshift to 3rd, no matter how high the engine revs. I tried it last night and got scared after it still wouldn't upshift when the engine was screaming bloody murder at...oh, about 6300rpm!! That's way past the engine's limits (stock L69 except ignition and exhaust).
Here's the other thing I noticed. When I checked the fluid, it was full, but the dipstick came back up with bubbly trans fluid. I do have a 4,500lb-rated trans cooler on it, so I hope to rule out heat issues.
Could the absence of the upshift and these bubbles be related?

 

I guess I would start with getting rid of the Superior (NON) shift Kit and get a TransGo Reprogramming Kit in there first. See if the Governor or bore is worn or the nails that the weight run on. Does it just do this on the 2-3 shift? If so the 3-4's could be seriously on the way out but not totally gone yet. If that is the case it is O/H time.