My uncle bought an 88 samurai 1.3 liter. The guy he bought it from said he put a transmission in it to where his grand children could drive it. The rig will not go over 30 mph and he said it is not geared in the rear end. My question is can the Sami be governed? Is there a part in the transmisson that can be installed to governed the vehicle? The timing is good runs and drives just revs out at 30 mph.

The limit with vehicle modifications is either your skill, or your wallet - anything can be achieved if you know how to do it, or are willing to pay someone else to do it.

The problem can range from the engine having low/no power, the transmission could be defective (slipping if it's an automatic), a slipping clutch (if it's a manual), the transfer case in L4, or poorly chosen axle gears.

Do you have a tach on the vehicle?  Do you know what rpms the engine is turning at 30 mph?

It sounds like the transfer case is in low range.

whats stopping it? is it revved too high ?

If its revving out in 5th gear at 30 mph your transfercase is in low.