98 K1500 silverado U joint confusion.

[FASTOYZ]

I have a 1998 chevy silverado K1500 Z-71. I am trying to replace the rear driveshaft rear u joint as it has some slack in it.The u joint in it now is a factory 'spicer' u joint that has a c clip installed on the INSIDE edge of 2 of the cups. These cups are the ones that rest in the clamps on the differential. I assume that the c clips on the inside of the cups are strictly for centering the u joint as it rests in the diff clamps. I have noticed that all the aftermarket u joints do not have these c clips on the inside of the cups to hold the u joint center. Is it ok to assume that the u joint would stay centered simply by clamping it in to the diff clamps? There are no bumps or anything in the diff clamps themselves to keep a u joint from sliding out of center either.

I have also learned that there are 2 sizes of u joints depending on if you have a heavy duty chassis or not as I got the smaller size first & realized I need the bigger one. The truck is a Z-71 & does have a trailer towing package so I'm assuming that makes it a heavy duty chassis? The truck also has an aluminum driveline if that factors into the equation at all. I am the original owner of the truck so I know all parts are factory.

Thank you for any & all input.

Chad