You say it happens at 55mph(ish). At that speed you in 4th gear and the TC is locked. If youre on fairly flat ground then you might be experiencing the point where the truck isnt pulling but also isnt quite being pushed.Your at a speed where the engine doesnt have to work but also isnt been dragged to raise RPM ( as if you were decending a hill)Kinda like a floating point/free wheelin. If you can understand this and it makes sense...THEN ITS NORMAL!!!! :doh: send me my damn pedal back!!:hehe::Cheer:
Aint this fun?