Gear grind after fluid change

A833, switched to the Redline GL5 shock proof and it grinds shifting into 3rd gear. My guess is the stop ring on the syncro is not slowing down fast enough to meet the speed of the gear due to the slipperiness of the full synthetic GL5. I have a GL4 Redline MT90 sitting in a jug, do you guys think this will make a big difference or am i just wasting time and money.