Hi, I drive a 2006 Ford F-150 4x4 XLT with an automatic transmission and the truck has 83,600 miles with 18" rims with 35" tires and a 2'5 inch leveling kit. In cold weather the truck has been feeling like it is miss firing for about a week and half now. So i bought new spark plugs and a fuel filter and still have 1500 until my next oil. When i was driving to work( about a 15 min drive) yesterday i got on the highway and was accelerating and the truck made a hard shift and a klunking noise. After that the transmission started slipping and the truck wouldn't go over 45 mph and the over drive light started coming on and off. I pushed the over drive button on and off and it wouldn't do anything.so i kept driving and the truck would stay around 45 mph and not let me go faster. then i had to make a left hand turn and slowed down to about 10 mph and the truck started accelerating really slow and wouldn't go over 10 mph. So i pulled over and turned off the turn and sat for about a 1 or 2 mins. Then started the truck back up and took off and the truck accelerated to 30 but wouldn't go any faster. I had about 5 miles to still get to work so i just went slow but the rpms were running about 3000-4500 going 30mph. Then i hit a hill that the transmission start making a burning smell. it got to work and it took me 40 mins to get there. I parked the truck and checked the transmission fluid it smelt burnt and was a really dark dark red. So i left it at work and went to start it up today and see what would happen and i tried to put the truck in reverse and the truck went forward and same in neutral but when in drive the truck wouldn't move. I am just wanting to see if anyone has an idea of what it might be. Thanks

 

Time for a transmission rebuild. It's burnt.

 

If you had stopped when you started having problems you might have been able to get the trans repaired. Now I suspect it's burnt to a crisp. It is going to need a rebuild to ever work again.