You can do a bit better. I think Sennix has a 3.73 and he is DPF on with the banks. I don't think there is much down side to the Delete tuner with mild tunes. 50 HP or so. At least I don't recall anyone talking about them. Of course you lose the warranty if you have one. And it is a federal crime. And a PITA if you have to go back to stock for an emmissions inspection.

My truck is a 4.30 with DRWs. I deleted for less than your stated budget. Bought a used tuner from Craigs and a pipe from ebay. $600 plus I had to buy a sensor beecause I couldn't get one out of the old pipe. I don't have a lot of data yet but I'm getting 10 MPG towing on three trips, a 1 to 1.5 MPG increase. On my last check of mixed driving half highway half city I got 14.3 and that's the best I've ever done. Again a 1 to 2 MPG increase. That's probably the best I'm gonna get but you should do better with a 3.73. I think given where the price of diesel is going a 10 or 15 percent gain might be worth it.