98 Jimmy Tranny issues

Been working on my Mother In laws 98 Jimmy past 2 weekends now. Changed fluid and filter, then it threw up a code P0758 replaced solenoids 2-3 (both of them) still throwing same code replaced modulator on tranny ( computer looking thing). Still throwing same exact code. It is like it is constantly running in 3rd gear unless you manually shift. If i turn it off and back on it runs fine until it runs through gears and then it will not downshift without it being done manually. Please help me out on this.

A proper diagnosis is in order here, make sure you have 12v at the big connector on the trans and the contacts inside are clean. Then you should have the trans road tested and scanned by a pro with the appropriate trans function bi-directional scanner.