Hi Carl, i’m a bit like yourself, i’ve played on guitar since the age of 15, then i swapped over to playing the sax 4 years ago,
the sax is so much more challenging so i stopped practicing on the guitar as i couldn’t find time to do both.
In terms of backing tracks, i found the best thing to do is get some software that slows or speeds up the backing track to a speed that you can play at without making mistakes – it takes out a lot of the depressing stress out of trying to practice tricky pieces at the proper speed. Practice them at slower speeds, until you get a piece error free – then up the speed later on.