[wantabe351]

Do yourself a favor and before bring it back or having someone else work on it,ck the gear selector lever/linkage at the trans.If not set up correctly, that will cause the problems you are having..Pop the shifter cable off(out of) the lever.Parking brake on,truck off, the eye on the lever should line up with the end on the shifter cable(both in park) if not the cable is adjustable..give a try first before messing around with the VB...

 

[5.9x2]

What Shift kit did your trans guy install? I haven't heard a lot of good things about BD stuff but they have been around a while. I would look for a valve Body from one of the many site sponsors here. How low is the Stall on your new converter