Similar problem - played in a duo with BIAB/PT backing tracks until a few years ago. Lots of bar chords on the electric although the finger soreness only really affects the acoustic stuff with heavier strings. Came out of retirement for one gig and playing chuck berry shuffle for several verses caused a complete cramp in my arm!. Had to stop before the song finished. The best exercises are actually doing it I think. Mind you a while back I had awful back problems and was prescribed ibruprofen gel. Before we went on I rubbed it generously into my back. Ten minutes into the set began to lose the sensation in my fingers until they went completely dead. I'm not the world's greatest guitarist but that night i was probably the worst.