High RPMS at 55 MPH

Ok, so pulled Dads cuda outta storage today. Of course it started pouring about 20minutes later....but definitely "seems" to be over revving....approx 3500 @ 50 mph...doesnt seem like as firm a shift into 3rd gear as it is into 2nd.
Tires are 245/60/15
I havent verified the rear end gears, but I will chk that tomorrow as well as the recalibrated factory tach against a new one we bought a while back.
Gears as far as fendertag goes are 3:23.
As for the torque converter, the prev owner had the orig torque converter for the 904 273 commando. But when he put a 400 hp 360 in it, a new torque converter was installed. This new torque converter is the one we went with. If I remember correctly I ground off the weight for it to be used on the 273 that is in it now. We used it as when we put the cam in Dads 273 we put in comp cams 270S. Im going to try and "flash" it tomorrow and gauge what stall it is.