I was looking under my Jeep, with the NV3550 transmission, today as to what I needed to change the transmission fluid. Surprise, surprise, hex plugs, 17mm I believe, what next. 1/2" drive would have been too easy. Anyway, got a set of hex bit sockets (1/2" drive) at Princess Auto (Canadian) this evening, on sale luckily.
The NV3550 is an interesting transmission. Here's a site
In 2000, Jeep began using the NV3550 in Wrangler TJs and Cherokees. It has become the medium duty 5 speed of choice. It is plenty strong for a medium size small block V8. All five gears are fully synchronized and shift very smoothly and easily.
This unit is conservatively rated by New Venture Gear at 300 ft/lbs torque handling capacity. The NV3500, used by GM and Dodge with V8 engines, is an earlier version of the same transmission.