I used my stock 4.0 pump for years with Hydro assist and a very large cooler and it worked fine. I did drill the pump port over sized buy two steps and again I ran a very large cooler.
I was able to push 39's around with little problems and I used a very large ( for hydro assist ) ram, it was a 2x8" ram so it was a lot of body to fill, but again no problems from a stock T/C pump.
Kits are nice but stock does work with the right stuff and a little tweaking to the system.
1993 YJ 4.0 60 Front, Rear steer 60, bolth spooled, 5.38's, 700r/241 39.5 iroks and beating it like it owes me money.