95 G20 4.3 Trans won't go in 3rd.

Van was parked for about 2 months, and now it won't go into 3rd or OD. In the past it has been weak holding interstate speeds.
Any ideas?
thanks.

Van was parked for about 2 months, and now it won't go into 3rd or OD. In the past it has been weak holding interstate speeds.
Any ideas?
thanks.
Any check engine lights on?
Check fluid level and condition.
If ok.
YOU NEED TO GET IT ON A TRANSMISSION/ENGINE CAPABLE SCANNER
Read out transmission shifting and check for codes.
Post back any engine or transmission codes.