Ihave a 1988 f250 with the c6 automatic trans and my problem is it is running at 6000 rpm at 65mphand icant figure out the problem i,ve changed the vac mod and it hasn't change it also shifts at the at high rpm's.i changed the fluild and filter twice a pop88

SOURCE: 99 f250 SD 7.3

Your speed sensor in your trans. needs to be checked out sounds like its not working or not getting a good signal until its generating enough power and speed to start until it reaches 30 MPH. Check that out sometimes it could just be some dirt on it. It all makes sense the ABS light is on because its not reading the speed of the tires, and the AOD light is on because It has no idea when to shift into overdrive without knowing how fast its going. I sure Hope that Helps You Out, And Thanks, Bear001

SOURCE: 1999 ford windstar sensor problems on 3.8 engine

iac valve is sticking remove valve and clean the shaft so it moves freely. This is a very easy fix.

SOURCE: automatic transmission not shifting into 3rd or 4th

call a dealer and they will tell you you are suppose to change your transmission fluid every 2 years or 30,000miles but if you was carrying this much load you may have over heated the transmission so I would shop around and get a good deal at a transmission place where they can replace the filter and the fluid and adjust the bands on the transmission if needed

SOURCE: auto trans shifting VERY HARD, possible cause?

It could be several things but I will give you a few ideas anyways to try and avoid the costly Ford dealer mechanics. Check your transmission fluid to make sure that it is full and that is still good and red. You may also want to just go ahead and change your transmission fluid but when you do so remove your transmission pan. Inside your transmission pan is your automatic transmission fluid filter screen. Make sure to clean it thoroughly and put back on filling the transmission with new fluid. Cleaning the screen is probably the most likely thing that will help. You also might want to consider using a transmission fluid additive that will help it shift easier. I've had pretty good luck with Lucas's products. Hope this helps. Be sure to let me know how it goes and if you need more help clarifying. Goodluck.

SOURCE: Hard shift from 1st to 2nd. Engine rpm goes to 3000.

the tranny is slipping ,,in other words its starting to go.