Okay, so I have an 04' Lariat 2wd with the 3.55 LS in the 9.75" rear end. Tires are currently 33s, probably going to stay at that size from now on. I have a hum from 42-50 miles an hour only while on the accelerator pedal. It goes away after 50 and comes back at highway speeds. Does not seem to be tranny related since I can drop out of overdrive into 3rd and there is no change. So, the goal is to get the rear gears redone, however, I want to change gearing. I do 95% of my driving in town with little to no highway. I also don't pull with this truck too often, that's the 350s job, but it does see a trailer of 5-10k every once in a while. I was thinking of going to either 4.10 or 4.30 but really not sure and would like to see what effect it had for others on in town mileage and highway mileage as well of course as acceleration. Current in town mileage with mods is 12-13. Highway is 19-22.

Also can anyone explain the slight interior shake at idle? Doesn't seem rough or like a miss. RPM bounce is about 590-610. I'm thinking a tiny vacuum leak just haven't bothered trying to get under the hood to hunt it down (I'm short and can't see under it without a step-ladder haha)