Won't shift into 4th. O/D light started

[BryanH]

I ran 18hrs straight (Empty) to Northern Indiana 1300 miles. Hooked up to 9000ils and started back. After 10 city miles I got the hwy. On the entry ramp the truck would not shirt into 4th and my o/d started blinking. I got worried and finally shifted. But I did not want it to downshift so I did not slow under 50mphs til Missouri (550miles) Light blinked the whole trip and when I slowed down to make the ramp turn and after some foot petal messaging I got it into 4th.
My question is, Knowing the 4th shift problem, I think it is clutches and I should probably rebuild. Does anyone think it could be a bad sensor or something else??? I have got 311K pulling miles on the truck.
Do y'all think I am on the right track?? I do not think it is the converter b/c it's just the 4th gear shift????????

[BryanH]

Originally Posted by BryanH

I ran 18hrs straight (Empty) to Northern Indiana 1300 miles. Hooked up to 9000ils and started back. After 10 city miles I got the hwy. On the entry ramp the truck would not shirt into 4th and my o/d started blinking. I got worried and finally shifted. But I did not want it to downshift so I did not slow under 50mphs til Missouri (550miles) Light blinked the whole trip and when I slowed down to make the ramp turn and after some foot petal messaging I got it into 4th.
My question is, Knowing the 4th shift problem, I think it is clutches and I should probably rebuild. Does anyone think it could be a bad sensor or something else??? I have got 311K pulling miles on the truck.
Do y'all think I am on the right track?? I do not think it is the converter b/c it's just the 4th gear shift????????

PS- Made it home with the load. After I droppped it the truck will shift but I still have to foot work it.