It's going to be very hard to match the performance of the 5.7. I have one of the few that held up good and plan on installing it in our new trailer when the warranty is up.
The new TT has a Shureflow Revolution 4 pump. It works good, has decent flow and provides a nice shower experience. It works well for 1 item being used (sink, shower, toilet) but I can't use multiple items like I could with the 5.7 nor does it make nearly as much flow and pressure.
There are some better but way more expensive marine pumps but the Revolution does a good job for the price.