Might have to move your front nav. light with side lights then mount in the center with a quick release mount. I would never mount a unit on a rail will not support the weight or the torque it will generate you could see the whole thing go overboard. o_O just my thought thou...
Sounds like you are dogging it out of the hole what rpm's are you doing at wot? I'm thinking you might need a 13 or 15 pitch prop. Plus what year is your pontoon and what year is his.
If your only running a trolling motor should be fine as long as the td is deep enough. I did run a portable ff. Off the back of a 12ft. aluminum for a while and worked out just fine was on a bracket that mounted to the transom but you really can run any where you want to just make sure it is...
Do not be cheap buy the right stuff they run them on the jeep winches and they are pulling a lot more force than loading a boat.
When I did pull with cable not for boats but off road winches would always throw a jacket over the cable in case it snapped did snap one time came flying back faster...
Try Trollingmotors.net they know what is what I just pickup a Terrova 55 unit from them great service and answer all questions. I know with the Terrova unit you only get 2D sonar on the ff, But if you upgrade to the next unit don't remember the name the sonar will do a lot more.
If you buy one of those space type reflector blankets and throw it over your sleeping bag will keep your sleeping bag dry. And you can enjoy the night sky use to do that in a friends 18ft. aluminum boat launch at night when we got off work fish a little then sleep on the floor. Wake before light...
I would think you just have to bite the bullet and buy another circuit board for it how old is it? Plus you are right about the TMs with GPS I just got mine hooked up and love not dropping a anchor MK Terrova.
Wish I could help you with this but never done any salmon fishing myself I think there has been a few on here that have. Hopefully they will give you a reply if you go would love to see some photos of the salmon you guys get.
If you changed cables and cleaned all your grounds could possible be the switch. Is this a new boat to you or it has worked good and just started with this problem?