ok i have a 420a with a rebuilt transmission.
while im driving down the highway and start to go up a hill it will shift out of overdrive and the tach will go up to about 3500 rpm, then it will shift into a lower gear sometimes and the tach will jump up to about 6000.
im assuming this is not good for my engine so i usually let offf the gas so it will shift. but what i need to know is where and what is the problem?

 

have you checked the fluid? if it is low it could cause it to shift funny

 

How long ago was it overhauled ? or replace wiyh a reman?

 

i havent checked the fluid but i will make a note to. and it was rebuilt about a year ago, but i dont know what was done to it

 

so i think i may have found part of the problem.
one of the fans on my radiator wasnt working, it was stuck in the radiator and the fan was all ground out from it trying to turn. so i replaced it and my car seems to run a lot better now, i think the fan was restricting airflow and not keeping the engine cool enough, i never had a problem with overheating but this seemed to help my engine run better