Replacing front pinion seal
 

How hard to Replace front pinion seal on 2000 gmc jimmy diamond edition 4.3lt 4d 4wd

It's not really that difficult if you know what you are doing, but once the driveshaft is off there is a big nut holding the yoke on that will be very tight. Then the yoke may or may not need to be pulled off the pinion with a puller tool - some do, some don't. Once the yoke is removed, you pry out the old seal and use a seal installer tool to install the new seal (or if you are experienced you can pound it in with a hammer). Inspect the seal surface on the yoke for wear and replace if any problem. Install the yoke and tighten the nut to maybe 150 ft lbs - something below the torque that will further crush the crush sleeve in the rear end (The original crushing of the sleeve is a critical adjustment so don't want to crush it further - but not so loose that the gears will have extra play). Hope that answers your question.