What kind of mpg increase can be expected with a tonneau cover on a tacoma? how about an aftermarket magnaflow exhuast? While I have some interested parties looking at buying my truck they have been lower than what I wanted to accept for an offer. So I am trying to get better mpg in the mean time. I have already done the basic stuff: tire pressure, all synthetic, slowed down a bit on the highway, guage traffic lights etc... but I can still only get a combined highway/city 18mpg. I guess thats ok for a truck but not great.