Best tire pressure for aftermarket tires?

I always ask the guy (if I remember).

Same as the weight of the vehicle has not changed.  You have lowered the air cushion height of the tire so it rides more like a go cart.  The walls of the tires are all going to say 32 whether it be a 17", a 14", a 12", a wheelbarrow tire ( so the 32 just means do not inflate much past this number.  It is a tire number that is in the mold of all tires, but there is a difference in weight from say a HUMMER and a SMART CAR and yet the tires have 32 psi on them.  Being the cars are different weights check in between the door opening to see what the sticker recommends for your vehicle.  Manufacturers of the car know what their vehicles weigh.

I agree with everyone who said 35PSI. You can always inquire with a local Chevy dealership and I'm sure they'll be happy to help you. 

35 - 45 psi is generally recommended for a higher ply tire, or higher load. A 275/55/r20 is not designed as work tire and I suspect a lower pressure would be better.

I'd recommend getting in touch with the manufacturer of the tire and tell them what you've done and go with what they suggest.

If it were me I'd be running 32 psi at most as I suspect 35 psi rattles your teeth when you go over a cigarette butt with those new tires.

Start with the 35 PSI recommended. If you want a firmer ride use 37 PSI.

You should use whatever the professional that installed those tires recommends

You use the exact same pressure in any size tire you install. If the manufacture recommends 35 then that is the pressure you use. That recommended pressure is based on the weight of the vehicle and the load it carries. BTW, the pressure listed on the sidewall of the tire is the maximum pressure the tire can safely handle and is NOT the recommended pressure. 

Try reading the wall of the tire. All manufacturers print their recommendation on the tires.

I'd go with 38 PSI

You want the correct PSI in every tire?  You need to do your homework.

Weigh how much weight every tire is carrying.

You talk to the tire manufacturer to find what PSI is required to carry the weight.