Could be a couple of things. Shifter linkage binding up, or the shifter arms and/or shaft on either end of the linkage catching on something and binding up. I would start there first. It could even be a broken spring or pawl in the tranny, which would cause the shift lever not to spring back up. Make sure the linkage and bolt at the front aren't catching the motor fins. I have the 113 in a Fatboy and its really close. The motor is already wider than stock and add a little heat and its going to expand a bit more.
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2015 Denim Black RG, FM ss ceramic coated 2-1-2 pipe, White Bros Original E Series Mufflers, FM ac, PV Tuner