Fixed ATX slipage by disconnecting plug under hood ?

[driftn240]

Ok, here it is. I have a '90 fastback with auto transmission. Since I bought the car($600) I've had slipage going into just about every gear. It doesn't slip at the same time every time, but I'm talking like a 500-1200 rpm slip(that's more than just a small slip). I've been thinking about; looking into a new converter, having the speed sensor looked at(at a dead stop the speedo will go up as I give it throttle,in P,1st,2nd,3rd,and overdrive), or take it to a garage to have a trained tech look at it($$$). OK, this is where it gets weird to me. I was looking at 240sx.org in the FAQ, and came across a FAQ called SHIFTING FASTER w/ an AUTO. In this FAQ a shift kit type effect is described, by just unding a plug under the hood. I thought what the heck and tried it. This seems to work just as described. The weird part is the the slipage is gone to. Is there a possibility that by uping the pressure(as stated in the FAQ) that my problem is gone? Could my valve body be worn or just REALLY gunked up? It doesn't make any sense to me but the slip is gone. I'm not a new car guy I've had 2 years training, worked the feild for 5 years, and am in the prossess ofASE certifcation. But I can't think of a good way to explain this 1 or figure out the real problem I have. ANY thoughts here would be a real help. THNX.:help