i have a powerglide on my '62 and when I'm cruising on the freeway and let off the gas coming to an off ramp, the tranny automatically downshifts way too early. Right around 40mph, and the rpms shoot way up to around 4500rpm. it does it occasioanally around town too. Not only is this very hard on the engine, it's extremely annoying too. Is there a way to adjust this?