Yesterday, I noticed the Castrol GTX HM at a Checker/Kragen store while I was shopping for a HM oil out of the group of heavy 10W-30's, (Chevron, Havoline, Citgo, Pennzoil) that run about 83 cSt @ 40C.
These heavier HM oils noticeably reduce the noise at startup for my Silverado 5.3 Vortec engine.
Chevron was $1.99/qt & Havoline was $2.19 even though the product data sheets list identical numbers, with the exception of TBN, 7.9 for Chevron & 8.0 for Havoline. Go figure!