Like you I had a 35' TT from hitch to bumper that the family used for 12 years. We bought our first 5er this year coming in a 42' in length. I bought B&W Companion 20K hitch, made sure I'm set up to tow level, and I have to say towing the 42' 5er is so much smoother than the 35' TT. The 5er just feels so much more stable and I was amazed at how much less movement side to side I get from the 5er than the TT. The biggest adjustment for me from TT to 5er was learning how the 5er tracks the TV in tight turns and with backing into a campsite. If you have a long bed truck, you turning radius backing up is great! The best advise you will get from anyone is go to an empty parking lot, put out a couple of cones, and practice backing up until you can put it in the same spot three times in a row. The second best advice I got for backing is take your time when backing in and don't be embarrased if you have to circle the block to get into a better position before backing into site. It is better to do that than damage your new 5er, TV, or someone else's property.
IMHO if you do the upgrade to a 5er you will not regret it!