Automatic transmisson

My 94 Dodge Dakota will upshift into third gear until it his 34 mph. Whether I am going dowm hill or just driving. How can I get it to shift.

Confused. You say it upshifts at 34 mph then asks how to get it to shift?

Do you mean it won’t upshift till 34?

or what? PS, how many miles on the car? what engine?

I would check the fluid level and then look for a stuck detent cable or rod, then call for help from a transmission guy. Oh, that’s right, there’s a few of them here.

Some automatics, all of the older ones, use a vacuum modulator. It measured manifold vacuum and changed the transmissions shift points. If it is defective or the modulator is not getting vacuum (hose slipped off) the transmission thinks the throttle is wide open and doesn’t shift until the engine revs real high. A lot of modern automatics might use computer signals instead of a vacuum signal. Some older automatics used a mechanical linkage that told it how far the throttle was open instead of a vacuum signal. If it gets unhooked from the transmission, the transmission shifts weird.