Hello, i have a 1993 plymouth voyager, it has a 3.0 liter v6, the transmission is vibrating at around 45 mph, i have been told that the tourqe converter is not locking up properly, (3,speed,with no overdrive, just lock up converter)i bought this van a few weeks ago(from one owner) he has gotten transmission rebuilt twice(98 thousand miles, 2001, 140 thousand miles, 2003) both for same problem im having now. So is there a fix? I know Chrysler screwed up those years on transmissions. Also, the 3.0 liters in the vans(around 22 mpg) is their any way to increase the mpg, its tuned up, but i was thinking about pulsar plugs and maybe a cold air intake, and also amsoil, synthetic motor oil, i like the van, want better mileage, but wold like to figure out the transmission issue, i was also told the transmission needs to be "tweaked "for to work properly, but not sure what that means