Questions in general
 

How many miles *should* I be getting per 18 gallon tank with my 292? Also, would a longer exhaust system that extends to the rear wheels as opposed to under the cab make a large difference in performane?

What is the best way to get the inside of the cab to stop vibrating when I take off. I can't really tell where it is coming from, since the sound telescopes all around the cab, but I plan on laying down some dynamat inside to see if that helps. Would I have to remove the dash to put dynamat up inside of it? The vibrations in the truck don't bother me too awful much, but I plan to have a real nice sound system in there once I get the fuel tank removed... and I want it to be almost silent in that cab if physically possible... I know all of you gurus here have done it... any economical tips?

Robert