SRW vs DRW milages

[reddrum]

I saw an old thread on this but there were no real answers so I'm posing it again.

Can anyone give real world what a DRW vs a SRW mileage is? It'd be great if anyone had experience with an LMM but I'll take anything I can get!

I'm thinking of changing to a DRW to get additional GVRW but I'm scared how bad the mileage may fall off.

thanks in advance

[06nighttrain]

Reddrum,

I have a "01" LB7 DRW 3500 and a friend of mine has a "03" LB7 SRW 2500. I usually get 15.5 to 16 mpg and my friends truck gets 20 mpg (unloaded of course).