A while back as in I haven't followed Monster Trucks that closely in years, he very well may still be building complete trucks but I haven't heard anything recently regarding that, there are many people around here that would know way more than me on the subject.
While a CRD and a Cohen may look similar, they were developed by two totally different people. Paul Cohen designed the Cohen and I believe was building them solely for Monster Jam up until recently, CRD is Carroll Racing Development, founded and owned by Tim Carroll. There have been MJ trucks that have run them but also many independents. Last time I heard Paul was building Cohen's for anyone and I'm sure some independents run them now.
If any of this is wrong please correct me.