I have a 1999 F350 that I have a tranny gremlin that has been driving me nuts. I even had the tranny rebuilt by Brians Truck stop and we are both stumped. To be clear Brian has been fantastic trying to figure this one out and I am very happy with his service.

The symtoms are as fallows. I can jump in the truck and drive it around for a while and all is good. If I pull over to say buy coffee or run into a store, after the truck is warm, when I drive it it will slip off the line. If I pull it down into 1 then it will take off no problem ussually, some times not but that is rare. We have dropped the pan and it is totally clean inside, replaced the solenoid pack and that did not change anything and replaced the black electrical shifter deal on the side of the tranny. Nothing has made any difference. It seems to happen worse when it is warm out so I really want to get this figured out as boating season is almost hear. Any thoughts on this would be fantastic as I am loosing my mind!

We also replaced the speed sensor recently.

i know this will sound crazy,replace the filter inside the pan,i saw that happen once.good luck.

Mike thanks for the thought unless I got another bad one then I think that may not be it?

from my experience trans slipping is from heat. are the cooling lines to the radiator bent or kinked? check the coolant to see if a leak is there, lack of pressure and heat are usually the culprits and if a band has been scorched, unfortunately it may have to be redone again.

I have not checked the coolent lines but the fluid is totally clean and there is no evidence of overheating. I can run it all day long if I don't stop just when I stop that I have to cross my fingures.

Not that this will help....but I have never seen good luck with rebuilds. My friend had a 97, went through three before he bought a ford one with a warranty. 5 years later no problems. Another buddy had a 99, went through a rebuild, then bought the ford one. Had another guy go through 2 on his 02 and finally bought the ford one. I just haven't ever seen anyone rebuild them without any issues. Ford sells units with a warranty, cost more, but in long run seems to work out. Sorry this doesn't help you.
Wonder if when you replaced the speed sensor a wire got crimped or messed up a bit. Though i think you would see that more than just first...

ZBO, thanks at this point any ideas are good! The guy that rebuilt this thing is known as the best. I researched the hell out of it. He gave me a 3 year unlimitted miles unlimited HP warrantee. I am out of that and he still has been sending me parts for free trying to help me out. I am thinking some kind of electrical issue but how the hell do you trace that. I hope that the scanner reads it for us like some one said on another board.

Depends on what is used in the rebuild. Transmission builders have come a long way in the last ten years. It's amazing what triple disc torque converters, new valve bodies and billet shafts can do...

Looks like I have an internal leak is the thought now. Bummer, I hope that Brians takes care of it.

The 4R100 you get from FOMOCO is rebuilt.

Sam