Im curently shooting a 20 shot on the 730, that only gave me 11hp at the wheels for a number of reasons.
One- the clutch didnt hold in top gear
Any advise would be good.

 

If you already have the HPR clutch, the only thing I can think of is stiffer clutch springs. You might want to find out what they automatically give you, and what HPR would suggest. Also, there are a lot of other reasons why you may not be getting horsepower you think you should out of your Nitrous system, in this case NX Express. Tuning the system is pretty critical.