As mentioned, the 4L30E transmission is a "sealed" unit and as such does not have a dipstick. The only way to check your fluid level is to use the "higher" of the two drain holes on the bottom of the pan. You *must* do this while the engine is hot and running, otherwise all the fluid will have drained to the pan and will come out of the top hole all over you.When hot, the fluid should come up to the top hole. Stick a finger in, if you can't feel fluid, use a syphon or hand pump to shoot some up into it.I own a '99 Troper, and would strongly suggest dropping the pan and replacing the filter, as you probably have over 100k miles. DO NOT have this trans flushed at a shop as the small galleries are prone to jamming with the gunk the flush will free up, and will cause the trans to fail.Excelent Isuzu info can be found on Ryan Endres excellent FAQ:
http://isuzufaq.ibctech.ca/Complete shop manual for the 2G Trooper (and many other cars):
http://rapidshare.com/users/OSBSEOComplete, online, illustrated (technical) maintenance parts catalog with links to OEM part numbers:
http://www.myisuzuparts.com/Hope this helps!