5.0 supercharged (the larger brakes). I have tried:

New rotors
New pads (change from semi metallic to ceramic)
Lots of brake lubricant on both slide pins and backs of pads

I get an obnoxious squeal on light pressure when braking >40mph-0mph. Left front only. Increased pressure stops the squeal.

Anything else I can try before replacing the caliper?

 

If it wasn't there before the new pads I'd change them to a different pad. I use Brembo pads and they stop well last forever and do not squeal. Oh, and they are cheep

 

When I bought the car, the dealer put all new oem pads and rotors on the car. So for me, it always had a left front squeal on first bite (usually after warmed up)

I put ceramic Brembo pads on all the way around as I was so tired of the insane amount of dust from the oem semi metallic. The squeal seemed to temporarily go away, but now it is as bad as ever.