'01 Blazer 4l60e shifting issues
 

Hello Guys, New member here looking for advice.
I had a 2000 GMC Jimmy 4.3 4l60e 2WD that ran and drove perfect until a wreck last year bent the chassis.
In an effort to recover the drivetrain, I purchased a 2001 Chevy Blazer that had a blown engine. I replaced the engine and trans with the units from the Jimmy.
Now my issue is that when the blazer is in drive, It wont upshift to second unless I manually shift it. There is no upshift to third, manual shifting or not.
Futhermore, The speedo is not working.
I feel confident that it is not a major tranny failure because the transmission worked flawlessly before the accident.
I'm about to begin diagnosis and was hoping someone might be familiar with this problem and could save me some time by pointing me in the right direction. I wasted days tracking down gremlins in a Mitsubishi Trans a few months ago because I didnt reach out for advice. Thanks in advance.