I have a 90 Sami with stock everything. It was sitting for about 4 years, and I am now trying to get it road worthy. When you are trying to get it up to speed, and you shift from 4th to 5th the trans seems to slip a bit. You can feather the gas a little and it seems to be fine. If you try to floor it, it will rev high. I am not sure how to check the trans fluid. Any help with this would be great.

Clutch?

Yes it is definietly the clutch..  You can get a new one for next to nothing. <300 for everything.

Or if you do stock you can get a clutch from auto stores for about 80-90.00

Or better yet if you want more holding power but dont want to spend 300.00 for a centerforce clutch go with a exedy clutch they have 30% more holding power over stock and usually can get them for around 100.00

I ran one hardcore offroading and highway miles and loved it.

Thanks guys! How involved is replacing the clutch?

Its really pretty easy to do, its a light tranny that doesn't fight to much when your pulling it out.
All the bolts are fairly easy to get to, one of my bell housing bolts was under the header but there was enough room to get it off. 

Oh and I pulled mine out with the exhaust on and it made it a little hard to snake the tranny out.
So I yanked the exhaust out when i was putting it back in and it made life a lot easier.


Hope that helps

Amilla

Before you go ripping the clutch out, try adjusting the clutch cable. It might not completely solve your problem, but you'll learn something in the process and you might put off the enevitable clutch changing process for a little while.

Here is a link to a clutch adjustment article:

http://www.acksfaq.com/samclutchadj.php

If you want to take a look at how to remove the transmission and change the clutch, take a look at the Factory Service Manual (FSM) at Ack's FAQ:

http://www.acksfaq.com/fsm.php

(Both of the links can be found through the search engine at acksfaq.com - use the link in my signature, below)

If you don't have a lot of experience fixing cars, don't worry - the Samurai is as simple to work on as they come!  It's a real good vehicle to learn wrenching on.

I hope that this helps!