Rattle Feeling In Gas Pedal?

[LRB]

I have a 05 v8 lr3. When I accelerate just before the shift from first to second I get a rattle feeling in gas pedal. Happens at higher RPMs but only at slow speeds. About 20k ago it was happening only when turning from stop at 1st to 2nd shift (just before shift) but now it happens alot more often and when accelerating even staight foward. It is getting worse and I am concerned it is a problem. Please any thoughts would help. Does anyone else expirience this. Feels like something is rattling under car but I dont hear anything. Thanks in advance. BTW I have 75k on truck.