Something was wrong with the 4000 converter or you bought a cheap one. Any price less than $450 for a 3500 thru 4500 stall converter means you are getting junk. I've got a good 3600 stall in my Nova Th-400/406 engine, drive it 75 miles one way to the track, race it 8-10 passes in the mid-11's and the tranny temp never goes over 165°. I've got a big 8" x 11" x1 1/2" thick stacked plate style cooler(they look like a heater core) and it is a good custom converter, not B&M, TCI, ACC, GER trash. Learned my lesson after two cheaper($250-300'ish) converters.