What tire pressure should I set my 33s to?

I just put some Boyfriend Goodrich 33/10.50R15 on my 1988 Ford F-150 lifted 1 1/2". What tire pressure should I set them at I put them on myself at work and I set them to 40psi but I think that may be too high. These are my first 33s I've had on my truck

That actually sounds about right. Got some chalk? Draw a line across the tread, go for a short drive. If the chalk wears evenly, it's good. If the center wears faster than the outside, too much pressure.