Need some help on my daughter's pickup. It's a 92 4x4 single cab with a rather weird but "Dad friendly" automatic (no burnt up clutches). I bought and went through it nose to tail. It was OBVIOUSLY a road driver...Had car tires when I bought and not a single ding in the underbody and original black paint and silver decal is immaculate!! Problem is.....Truck has plenty of pickup from the get go and can even bark the 32's I put on it, but seems to shift to third WAY too early and forces you to put your foot through the radiator to pick-up past 40, then once at fifty it is money, actually have to lift to stay 50 or it will head to 60 in an instant. Vacuum leak or kink? BTW, just serviced tranny and new filter...Shifted same before tranny service and with the stock tires. Any ideas?

Thanks....Bob