Heavy clunk on decel

[papageoff]

I have a heavy clunk that recently started a couple months ago and is increasing in frequency on deceleration that only seems to happen as I drop from something like 30ish  to a stop.  It feels like the transmission is sticking in a gear too long or something.  It's enough to physically feel it in the truck.  I don't know if it's related, but I have also noticed it seems to take a long time to move from R-N-D after I backup up a short distance (20' or so).  I'm not sure if that's related. 

 

I have 112k and do occasionally tow a camper.  I'm probably due for a filter change, but don't want to make things worse. 

I'm supposed to be towing the camper to VA next week.  Is it still safe to do that?  What should I check first?