I bought an RC truck chassis which has "Trinity T-Tech Modified Motor for Tamiya, Duratrax Blast Reversing ESC" (verbiage from listing; the motor and ESC are labeled as such). It is a strong and fast setup. But it goes through batteries like water in the shower. I am thinking about replacing the motor and/or ESC if I can get reasonable speed an power and a much longer battery life. It goes faster than I really need to for most robotics anyway. I am suspicious that the ESC is the culprit. It has a large heat sink.
My recollection of RC vehicles says …
you should be able to swap in a less aggressive motor. A 540 would probably be too slow, but, it is worth a shot. Better yet, goto your local hobby shop and ask the owner what he/she suggests.
More experimentation is making the motor seem more reasonable
This is probably a “rolleyes - duh” but smooth acceleration to a much lower top speed seems to make a big difference. While that may seem obvious, it actually involves having power to the motor for a longer amount of time. Right now, I am just messing around with it as an RC with a more expensive radio. Here it is in its current incarnation:
I call it the redneck robot (I was born in Alabama, so I am allowed to say redneck without insult :) ) since it has the big knobby tires and the cord. The cord will be going away momentarily; I just couldn't wait to make it roll around some. There is a Fio and a BuleTooth Mate in there. It is being powered by a 7.4v LiPo that is only 1380 mah. It came with a 7.2 NiMH that is 3000 mah and I just orederd another like it and a smart charger. I made myself a Dean's to Tamiya battery connection converter to give me a few more options for batteries. I am going to wait until I get the charger and new battery and see how it does with improved speed handling on a known well charged battery. The LiPo is lasting longer than I would have expected.
I took another shot with it
I took another shot with it “cord-less” 
There is actually something important in the picture from a possible replacement POV- notice that battery power is just going to the ESC. The ESC has a BEC that supplies power for servos and I use it for my steering servo. But I also have it wired to VIN for the Fio. There is a spot on the chassis for the NiMH packs, so once I have them properly charged I won't have a battery inside and would definitely prefer an ESC with a BEC.
EDIT - Purely for the sake of completeness, I should mention that I may put a small battery inside, connect it to VIN and connect the BEC output to the CHG on the Fio. Though it is labeled as 5V, I found some info at SFE that says it will take 6v just fine. What that would do is let me transmit a call for help when the main battery dies.