So with the stock exhaust I'm not seeing enough improvement to justify the mileage drop.

If I take it off, will I mess anything up? I remember my dad doing a TPS adjustment per Ivan's instructions but I forget if we did anything else. Can they be taken straight off?

"Can they be taken straight off?" Yes.

The X to Y factor. Say you have a map with more fuel than stock is that cell number. Here you go cruising onto that number with the Cell-X and the rpm-Y intersect as to no joy is about to happen with stock or no pipe out of the engine is the fuel is pre-before-pipe so how could you improve more mileage if the overlap of the engine's timing of both valves are open, heat is moving the fresh fuel out of the chamber; the close of the valves is now a lot of gas leftover and the unspent was flaming out of the pipe that the stock would have kept more of it back in there; or a fine line of flushing out the spent so the fresh is not lost out of that 'overlap' of the valves remain open and the rush of fresh out of the pipe is a given.

Do you want more mileage? Then run minus numbers on the X and Y so you are now back to a stock cell or even less fuel there... Watch the water-temp! Hear for engine knock.