If your "rear is jumping" (assuming I understand you) your rear shock is bottoming out and either does not have enough pre-load (more likely) for your 240lbs or, if you have adjustedI feel my rear keep jumping and turn slow , new one ask 400 I want find something cheaper
the shock's preload to maximum (as a test) and it still misbehaves ("bottoms out") it may have become faulty(truly, not very likely, but possible). If it were MY Bandit 1250 (and I DO have one) and I needed the rear shock replaced, I'd search Ebay for a few weeks for a low-mileage USED rear shock that came off the same Bandit 1250ABS model as yours and not go trying to put a different bike's
rear shock on your Bandit. I'm speaking from experience here as I did that very thing with my Yamaha FZ-1 and, although I finally got it right, it was the project from HELL and I wish I had
never bothered and would never, ever do it again.