CMX stuttering/chugging sound? HALP!
 

I built the CMX over a year ago now and it was left sitting in a closet at my parents house. It was built and finished entirely. I began to work on the body recently, a Jeep YJ from Tamiya and I figured to try the new LED lights I installed and run around the basement. When I went to do this I applied minimal throttle and the rig chugged along, kind of like a smooth roll then stutter, smooth roll thens stutter. Imagine a train whistle, hence the chugging along title. So, I did want anyone would do, begin a process of elimination. I rolled the chassis with the motor and driveshafts connected and the tires did not spin, they simply dragged across the table... static. I figured that maybe the motor mesh was too tight so I started there. Removed the cover, took a look at the spur and pinion, there was some play, but just to be safe I loosened it a bit more. Rolled it again, static wheels. Removed the pinion, the tires now rolled freely. But still, I felt some resistance. I then removed each driveshaft from the input shaft on the diff one at a time, both axles spun smoothly. I put it all back together, this time installed a Tamiya silver can from an ‘85 Hornet (a legit Mabuchi stamped made in HK) and though it sounded smoother it still made a bit of a noise, that chug/stutter. I’m at wits end, could it be the transfer case? Need to tear it open tomorrow I think. Please, if you’ve endured reading this far, enlighten me with what you think it is :)

Thanks!