I think that the Tight track is your problem with the boards and one of the disadvantages of installing metal gears as they get rid of the rachet gear you find on the plastic gearboxes an annoyance to most but i bet it wouldn't fry your board
the idler is definatly a must on these tigers with metal tracks and getting the tension right is another must as you've found out
another couple of options if you've done a lot of work to the tank is to get a tiger DMD/MF unit from the tammy and install it in the H/LONG tiger It won't be cheap but it is an option the other one is to go with Elmod and try that
To Date I haven't (touching wood as i say this LOL) burnt out one board in any of my tanks YET
but saying that all mine have the RX14 boards not the 13's
Regards Rob