Maybe memtestcl from the FAH community?
Folding@home - DownloadUtils
Other than that, most folks would just use whatever GPU stress testing program they could get their hands on (make sure you monitor gpu usage to ensure that the drivers aren't throttling it back) and RMA based on general failure rather than discriminating between GPU/Mem as being bad.
__________________
ASUS ROG Strix Z370-G Gaming (WiFi AC) / i7 8700K / 2X 8G XPG Spectrix D40 (3000) / XFX XTR 750 / ASUS Strix GTX 1070ti
AZZA Titan 240 / Custom WC / Intel 730 Series 480GB SSD / Seagate Barracuda 1TB / ASUS SWIFT PG279Q
Asrock AM1H-ITX / AM1 Athlon 5350 / 1X4G Gskill PC3-14900 / Intel 6235 Wi-Fi / 90W Targus Power Brick / Uncased 256GB Sandisk Z400S SSD / Mini-Box M350 / 24" Westinghouse L2410NM