I have noticed that on my 5.7 4x4 that if i accelerate fast while in tow/haul mode it stays in 3rd gear and will not shift to 4th unless i run it till it hits the rev. limiter. it will downshift if i come to a complete stop but then still wont pass 4th. the only way to get it to upshift is if i put it in s mode and move it from 3rd to 4th. has ...