95 auto cummins. Stock except for exhaust and intake. The guy I got it from said it had a built input shaft and torque converter. Has the lockup switch. Today when I was driving it wouldn't go into 4th. It would just scream in third. I put it to the floor (I was in a hurry) and it never shifted. I was running about 65 in third and when I let off the throttle it finally shifted. But then it just cruised in fourth and wouldn't go into od. I flipped the switch and let off the throttle again and it just cruised in fourth. I ran it up to 70 then let off, and it took a couple seconds then it finally shifted into od. I just changed the fluid and filter about 1k miles ago. Never had a problem before besides it not shifting right away. But it always shifted. Any help would be appreciated!!

Oh and I just put a new temp sensor in about 3k miles ago and my light is not coming on during this problem

 

Make sure you have the right level of fluid make sure the truck is warm and when checked in neutral dont overfill these trannys

and REALLY make sure your using the right fluid ATF+4

were did you install your temp gauge on your transmission

 

What are the air temps and trans temps? If the trans is too cold it unlocks the converter and drops out od OD to warm it up.
Most of us find the temp sensor on the trans cooler line and put a resistor in it.
I simply put an old rag in front of the radiator on my 95, worked great on cold days.

 

I meant the idiot light in the dash. And I just replaced that sensor a couple months ago. It is about 15-25* where I'm at and it's getting colder by the day. I used the right fluid and the exact amount needed. I haven't had a problem with it until it started to get really cold. Could it be that sensor again?

 

If you have the external lockup switch turned on, and the valve body is still stock, it won't shift 3-4 or 4-3. When the converter is locked, the valve body hydraulically locks the transmission into whichever gear it's in. It's an easy mod to change that, but it involves disassembling the valve body.

 

Mine must be modded then because mine goes into 4th no matter what speed I'm at and it will go into 5th on its own with the switch on

 

Dodge never did use a 5 speed auto. The last 'shift' is lock up.

 

dunno if this helps but when a bought my 1994 12v it struggled shifting into od unless I was out of the throttle. turned out my governor springs were bad on my p pump. pump was defueling causing a loss in power to get rpms right to shift into od. I could hammer down n it wouldn't shift into od until I'd let off about half throttle

 

EVERY 12 valve from 94 to 98 needs more revs. A gov spring kit will make you think you have twice the motor. Stock many of then defueled around 2200, let them fuel to 2800 or 3200 and see what you think of it. Above 3200 you should put stronger valve springs in them.