1966 chevy impala ss with 327 eng and 2 speed powerglide auto trans. Has recently started slipping after it shifts into drive. I've made sure the fluid level is up, replaced the screen and vacuum modulator. I've attempted to adjust the low band - I can make it stick in low, but cannot improve the slipping after it shifts into drive. Also, after it starts to slip, sometimes if you give it enough gas (floor it) it'll go like hell. Is there anything I can do to remedy this while the tranny is still in the car? I'm not a professional mechanic, but have been rebuilding my various old engines for over 40 years now and would like to avoid a top dollar overhaul. As a side note, I also have a TH 350 that I could put in here. Does anybody know if this would bolt straight in without any modifications? Currently get 15/16 mpg with the powerglide and would hate to lose that mpg. Any ideas??? Thanks in advance...