98 Blazer wont shift out of second. Any ideas of what it could be or what i can try?

 

recently I replaced my trans filter and must have it my 2-3 shift solenoid puting the pan back on. When I took it for a drive it would act like neutral when it should have shifted into 3rd. Replaced the solenoid and it worked fine. Until a week ago when it started doing it all of a sudden. I dropped the pan replaced again since under warranty but it did not fix it this time. If you find an answer let me know.

 

The OP's problem very well could be a solenoid issue which is a simple change after dropping the pan.

Your problem doobie could be a result of a damaged wiring harness in the pan.