That's pretty messed up.
A few simple things:
1) Lug nuts are tapered, are you sure they are being put on with the taper into the wheel?
2) Are you sure you have the proper lug nuts that engage the threads?
3) Are these custom wheels? Are they designed for a chevy of that era. Stud hole taper can vary meaning the lug nuts you have may not be fitting the wheel right. Also, the center hole from dodge wheels is slightly smaller and if the wheels aren't being seated against the hub all the way, you'd have major issues.
4) As thebeast says, perhaps they just aren't being torqued down proper?
These are all rather long shots, but, so are lug nuts coming off.
The only time it's happened to me was when I bought a '78 Ford Bronco back in the 80's and the previous owner had put some custom alum. wheels on it. He used the wrong type of lugs nuts for those wheels and within about 100mi, one of the wheels came loose while I was driving 60mph and thankfully I made it to the side of the road where literally the wheel then fell off (floped off). several of the studs were broke and the wheel was ruined. All because whoever put the wheels on didn't check what taper the stud holes were and also that the wheels didn't center mount on the hub flage like OEM wheels did and so the taper of the lugs was all that more important because they were now taking all the duty from all axis of force.
