The cheapest thing that you can do is to drain and flush your trans fluid. How long has it been since it was changed? Look at the fluid on the dip stick and see if it looks dirty. Smell it to see if it smells burnt. Get a fresh bottle of DEX III fluid and compare the two in color and smell. I haven't researched NSX auto trans fluid requirements, but on my other Hondas they require DEX III / Mercon fluid. You can go to Acura / Honda and pay $2.50 Qt or buy your fluid when it comes on sale at Schucks, Checker, Advanced Auto etc. for $1.29. Valvoline DEX III / Mercon even says on the container that it is approved for HONDAs, it is the same stuff only in a different bottle.
What I do is drain the fluid, clean the drain plug, it will normally have a lot of stuff on it, (it is a magnetic plug)
refill with new fluid to aprox normal level,
disconnect the line that comes from the oil cooler back into the transmission,
The way to figure this out is install a small length of tube between the removed line and the hard line, see which way the flow is going. You may have to switch lines. The object is to flush the oil cooler also.
The flow of the fluid is from the reservoir, into the pump, to the torque converter, into the cooler, back to the trans, through the valve body and clutches and back to the reservoir. That is the condensed version. The torque converter is where most of the fluid remains and is where most of the heat is developed. This is also why most Honda cars with automatic transmissions develope engine rear main engine seal leaks around 120-150 K miles. The heat from the TQ converter and engine heat cook the seal. That is why when I remove a transmission I always replace the rear main seal.
This is my method of flushing an automatic trans:
install a clear plastic tube on the return line from the cooler back to the transmission body. Put the other end in a empty jug,
open 8 - 10 Qts of new fluid, (whatever it takes to do the job),
install a long neck funnel in the trans filler hole,
get two other people,
one does the ignition, one monitors the fluid in the jug and color of fluid,
start the engine and let it IDLE,
pour new fluid in as the old fluid comes out, i.e. one qt out, one qt in..........
when the fluid coming out looks clean and new, you have flushed the transmission.
This is an exercise in crew communication and coordination!
This whole service just cost you about $24 for fluid and 4 empty milk jugs that you were going to re-cycle anyway! Or you can take it down and pay somebody $150 to do it for you.
You will be surprised how much of a difference clean fluid will make in any automatic transmission. This is a realatively cheap service that will extend the life of an automatic transmission dramadically (sp). Check all of your cars for their last transmission service. Don't forget that power steering too! You can do the same thing to it.
Next option.............rebuild the transmission..............OUCH sorry.