The best mod? that's kind of a toss up?
One of the following:
1)Mounting my spare tire inside the bed where it is actually accessable
I used a stock dual tank bracket, but I mounted the spare tire behind the wheel tub in the bed, because my "Tool box" is mounted in the front, additionally the 235/75-15 tires I run would not fit in the forward location.
2) the "Factory" sunroof (robbed from 1988 Eddie Bauer Bronco2)
3) converting my truck from 2wd to 4x4
4)While switching from a 2.9 flywheel & Clutch to a 4.0Flywheel and Clutch was "Good" swapping in the rest of the 4.0 and getting rid of the 2.9 entirely was better.
5)Upgrading the Original TK5 trans to a Mazda M5OD-R1 trans.
The fact that I managed to sell the Tk-5 for more than the conversion
cost me was icing on the cake
Worst mod? the pop open quarter windows on my supercab.
They never delivered the ventilation I expected, so in essence they were a whole lot of work for no real benefit.