96 Blazer wont shift out of OD

Hello guys, I have a'96 Blazer, Yesterday I took it on a 5 hr trip and about 2 hrs in when I was going up hill It started to lose power, If I pressed the pedal it would really die out. going along flat road it seems fine until I try to down shift (passing). I would have to pull over turn it of and restart and it would be fine til it went into Over drive. I am thinking it is not shifting out of overdrive. Any ideas? Thanks!!:banghead:

Is the SES light on? Any codes in memory? Have you checked the fuel filter for restriction? Have you checked fuel pressure and leakdown? Key on, engine off, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 3 to 5 minutes after the fuel pump shuts off.