I think its to do with the chain tension and your raiser links. I had a similar problem with my XT660R when i fitted my raiser links but i just found that the chain had to either be slackish or tight. I think you have it tight which means its rubbing on the rollers too much.

Either that or is your roller rolling? If not you will need to strip it and grease it and place it all back on. When you turn the rear wheel get someone to look at it and the wee roller should be rolling freely with out stopping if the can is in contact with the roller.

Hope this helps

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Plough on