If the sonic tester was calibrated I would not be so sure about chrome moly. .088 not a normal thickness. .083 chrome moly is normally dead on when checked with a sonic tester. Sounds more like mild steel .095 to me. I do tig all of my cages wheather cm or mild.
Drill a hole, take a drill chip and heat cherry red with a torch. Quench with oil or water, then bend if mild or break if cm. The 3 points of carbon in the cm makes it very hard and brittle. This is why you don't want to over heat a weld joint when welding chrome moly.
Red neck science baby!
Try it and let us know what you find............................Toni