1983 150 Custom Power Ram slant 6 help
 

Howdy folks,
I'm a newbie on this forum and just bought a 1983 150 Custom Power Ram slant 6 4x4 four speed. The truck is in great shape and only has 130,000 miles on her. She runs great as long as the road is flat, 65-70mph no problem. But as soon as we come to any kind of hill, the power is lost and we just creep up up. Big hills, 40 mph max and in 3rd gear, no 4th.
I have checked for vacuum leaks and all seems good. The engine seems to not be getting enough fuel? Like something needs to be uncorked for her to scream up those hills.
She is outfitted with the electronic fuel control system. Could that be the culprit?
Any help would be appreciated. Thanks so much, Atom..