8.1 Rattle Under Hard Acceleration

[MEGA14]

I have a 2002 Silverado CC with about 140k miles and the 8.1/Allison 1000 .

 

This year , the truck started making a rattling sound under hard acceleration . It will also hesitate to shift from 4th to 5th unless I let off the accelerator , leading me to believe it's all about the Allison .

 

Problem is , I sent an email to Sun Coast Transmissions and Ron replied that he could not think of what would rattle in the trans and suggested it might be an engine/timing noise .

 

If that's the case , why the hesitation shifting from 4th to 5th ?

 

The only thing that's changed this year is a switch to Amsoil from Royal Purple . The truck pulls as strong as ever if not stronger . The truck weighs about 9400 lbs. as it is a commercial vehicle . Only mods done are a CAI and the syn fluids everywhere .

 

One last thing : The engine light never comes on when this happens .

 

Any help would be greatly appreciated .