Tranny Problem its like its in "limp-in mode"

I have a 98 blazer 4x4. I just put in a 4.3L out of a 02 blazer. Runs great but when I got to shift the trans starts off in 3rd gear. I can manually shift it into 1st but then nothing else reverse works fine not burnt smell no engine codes or SES light any help??

How many miles on it?
How is the fluid level hot in park?
Was it doing it before engine change?
Have you check all fuses?

A good transmission capable sanner should show /have stored codes.
Post back any codes.