The 27-year-old, first capped by England against the USA in 2001, has been a revelation for Wasps since moving 200 miles south from relegated Leeds Tykes in the summer.
England wingers Paul Sackey and Tom Voyce also touched down for Wasps, while youngster James Haskell added a late fifth try for the home side.
"He was outstanding," said McGeechan. "I thought it was his best game in a Wasps jersey - he really caught the eye. I thought he also played well on Friday night against Northampton.
"We know how mobile Tom is and I've been critical in the past of his tighter play, but I thought he was first class in his ball carrying and his tight work.
"I thought for us it was his best all-round performance and his two tries capped things off."
Palmer's all-star show was marred by the worrying sight of England prop Phil Vickery limping off in the first half.
However, McGeechan revealed Vickery had simply bruised his buttock and not suffered a recurrence of his back injury, and was simply withdrawn as a precaution.
"Phil has got a bruised buttock and it was stopping him from scrummaging properly," added McGeechan. "One thing he wanted to do well was scrummage so we replaced him.
"He's fine and it's nothing to do with his back."
Scotland international Rory Lawson and England centre Anthony Allen scored for the Cherry and Whites but Gloucester director of rugby Dean Ryan was far from impressed.
"I don't think that's best we've seen from Gloucester in the opening half," said Ryan. "The game was pretty much over by half-time.
"Adams Park is a tough place to come back from such a big deficit. We got caught in the opening 40 minutes with a lack of decision-making.
"We were far too conservative and I think we got ourselves into a black hole which we couldn't get out of."