E4OD trans issue. no 4th gear

[echo]

I have a 91 F150 with a 302 and 4 speed auto. Overdrive seemed to simply stop working while cruising or under load. Only engages when going down hill.Everything else seems to work fine. Anyone know what would cause it to only fail under load? I know it's electronic so I'm hoping it's an easy sensor. But which one or ones would control the shifting?

 

[adsm08]

Probably a worn out band. It can grab, but when you try to make it do some work it starts to slip.

 

[echo]

Would any of the bands on an e4od be adjustable? If so how?

 

[Bent Bolt]

Only one band in a E4OD and it's for holding manual 2nd. If you have no 4th , being a 91 truck , probably worn out/burnt OD clutch. Especially if it appears to engage going down hill ( less load on the clutch )