I think you know you will be over weight once you install the hitch and hook up. So it comes down to does that matter and can you still travel safely. I think you know the answer to that question also.
Good for you taking time to figure all the numbers and ask. Many come here with a trailer too big wanting to know how to make their truck big enough/strong enough or fix a problem that can't be fixed without a new truck. Either make the jump to a 3/4 ton, look for an even lighter 5th wheel or stick with the TT's. Speaking from a TT owner that would love to have a 5th wheel (and will in retirement) but isn't ready to make that investment for the truck and trailer yet.