'90 E4OD wont shift properly

[Hway]

I have a '90 full size with a e4od transmission.I had it running doing 70 that was 2 years ago. I had to let it sit for a bit because of my surgery, then I took it out for a spin and I can't get it above 35 again.
I have changed parts over time.
I have changed the sensor on the pumpkin, changed the speedo gear, changed o2 sensor, alternator and a few others.
I even had it at transmission shop, they said it wasn't getting enough power but it was good.
Then I hit a bump then it was working right.
However since it sat for 3 months I can't get it running right.

 

[Tiha]

It sounds like it is an engine issue, not a transmission issue?

Not enough power to get enough speed or rpms to shift? Does that make sense.

Or what is it that makes you think it is the transmission?

 

[Jimbo26]

Go hit another bump, that'll git-er-done!

 

[Hway]

It sounds like it is an engine issue, not a transmission issue?

Not enough power to get enough speed or rpms to shift? Does that make sense.

Or what is it that makes you think it is the transmission?

The rpms is going high but will not shift. I thought when I took it to the transmission shop it would be transmission. They said it was good but it was the lack of power. I do know in later models a 3rd brake light would make it go in limp mode, so I checked all of my lights and if they were out, I replaced lights.
I'm not a mechanic but I'm willing to try to fix it.

 

[Hway]

Go hit another bump, that'll git-er-done!

Believe me I have tried that too.