High RPM shift
 

Hi all. I recently bought a 2004 Blazer and recently it started shifting at high RPMs going uphill and now it shifts at high RPMs all the time. It doesnt jerk into gear it just takes about 3000-3500 RPMs to go form 1-2 and 2-3 and it will only go up to 55 MPH. It seems sluggush taking off from 1st and R. I'm hoping this isn't a major transmission issue. The fluid level is fine. The codes I pulled were P0101 P0442 P0455 and P0302 (but a new plug fixed that one). Thanks in advance if someone can help.

my 93 s10 having the same problem too i feel like it not the transmisson at all either but something that cause it to slip