Have a 2002 f150 super crew with a 4.6L engine. Auto. Transmission was working great. coming home just slips when it goes into high gear. turn off O/D wont go into 3rd gear @ 45 -50mph running about 3500rpm any ideas what it might be. fluid looks good a tinge dirty but not burnt

 

I'd check the pan. Not everyone drops the pan, but just flushes the system instead. Very ell could have a good layer of grime in the bottum of it.

 

Maybe i should say it dosent slip it just goes into neutral. the engine revs up. wont go into 3rd at all even with the O/D off. with the O/D off it goes 1st to second and just stays in 2nd. with the O/D turned on 1st to 2nd works great but afer second it just goes to neutral

 

Rebuild time

 

You are losing pressure to the front planetary, causing no 3rd gear upshift. Sometimes, if you don't power flush them, you can drop the pan, replace the filter and tranny fluid, and still get some mileage out of them. It isn't a permanent cure all, just a sometimes fix. If doing that doesn't allow you a 3rd-4th gear upshift, then it definitely a rebuild situation. Anyways you look at it, it isn't good news. How many miles are on your truck. You didn't say.