I know this is an old thread, but just got a Tramp that has the exact same issues as the OP.  Wondering if there was ever a solution to the channel switching problem.  I have tried all the various one and two button foot switches I own-none make a difference. I've touched up the main PC board with solder and it generally works well except for low frequency oscillation on the gain channel if reverb is turned up (new tank installed).
Thanks.