Rumble on accelleration?

[MYSTICSVT]

I've got a slight rumble/vibration on accelleration that only occurs in 1st gear between 2250 and 2750 RPM. And it only happens when I'm towing my 14K pound Toy Hauler. The harder I accellerate, the louder and harder it is. It sounds like it behind the drivers compartment, my Dad who usually rides in the back says it feels/sounds like it's behind him. Anyone have any ideas of where to start looking? I got underneath the truck today and can't see anything out of the norm(driveshaft and carrier all seem to be perfect, no excessive movement). My buddy, who has the same truck, has the same issue. Anyone have any ideas?

Truck stats:
2006 F350 4 door crew cab, front leveled with 35" tires on 20" wheels. Currently towing on Innovative's Tow/Brake tune. Been in this configuration for 20K miles and it just started this problem recently. Truck currently has 39K miles.

[Deereman39]

I have the same problem and have not had any luck curing it.I am sure it is the drive line moving around but dont know why.
Ed

[goodriddance]

maybe a U joint?

[Raul@Stealth Automotive]

double check that everything is tight.... my guess would of been driveline vibration... so it could be many diff factors like the U -joints, axle wrap ect.... also when was the last time you balanced your tires? i had a slight vibration too and thought it was the driveline but i went and had my tires rebalanced and it went away....

good luck

[MYSTICSVT]

I figured out what was causing mine. I was putting too much air in my airbags and that was raising my rear end higher than normal. It must've been causing a weird driveline angle. Because I let some air out, leveled out the truck, and no more rumble/vibration.