Removing half shaft from 2000 isuzu trooper

https://www.google.com/search?q=2000+trooper+thermostat+replacement+instructions&rlz=1C1RNCN_enUS336&espv=2&biw=1177&bih=829&tbm=isch&imgil=MyxcE1lmoqOV-M%253A%253BiXVsmSpY-fs3TM%253Bhttp%25253A%25252F%25252Fwww.fixya.com%25252Fcars%25252Ft8392351-need_replace_thermostat_2000_isuzu&source=iu&pf=m&fir=MyxcE1lmoqOV-M%253A%252CiXVsmSpY-fs3TM%252C_&usg=__kclra7y8i6cHd5_Yo_8_q9MQfkY%3D

There should be a bolt where the tensioner pivots

If it is factory installed and you have a key with a chip in it.you will not be able to remove it.what happens when you try to start.

P0401 is EGR problem
P0300 is a cylinder 3 misfire.
Replace EGR valve and do a full tune-up.

Your SUV is really giving you a hard time, lol. Sorry but I've had those days too.
I would try to check if you have blocked EGR passages. If ok check for restricted MAP sensor vacuum hose/passage or restricted exhaust. I know you replaced the CAT but if the muffler is blocked then there would still be a restriction. Also check the wiring and connection to the MAP sensor.

Under the rubber boot inside the CV joint is a big spring clip round the edge , take this out and then the shaft pulls away from the axle with the CV on it .If you are fitting a new boot cut the old off if not just get the clips off and pull the boot back.

Did you take the shaft out from the wheel hub end too ?

First their are two different front axles in 1996 troopers. Isuzu changed the 4wd system from auto lock hubs to drive control axle.auto lock hube are on the older trooper's with the light and wiper switches on the dash. The same way to change both. Auto hub remove the six hex. screws slide off the hub remove the sirclip from the driveshaft. Newer hub has 6 alan-head screw's again remove them then the hubcap then the sirclip on the shaft and slide off the round spacer. Next 4 bolts from the lower balljoint and the brake's. Pull out the hub until it clear's the shaft remove the inner boot clips slide the inner boot out the shaft. Clean the grease from the end of the axle then with your fingernail feel along any of the 3 tracks in the axle and near the outer end of the track you will find a wirelike split ring slide a screwdriver under the ring and lever it off . Pull out the drive clean off the grease. You will see a sirclip on the end of the joint remove it and slide off the joint. You can replace either boot from that end. The outer joint is held on with a snap ring on the shaft inside the joint and is not easily removed need a hammer and drift to drive off the end and when removed its hard to get the snap ring on the shaft back into its place.You can change both boots from this end as well. Cheers

You force the nut of, and re-install with a new nut, or if still o.k use a puch to simulate the crimp, it is for locking the nut!

See illustration at www.myisuzuparts.com

undo engine mounts jack engine up as far as it will go