u joints please help

[Bleeblobz]

I am new to this site but not to silverado trucks. I have a 2000 standard cab 1500 long box with a 6.0 swap. Today I replaced the u joints. They were the plastic injected stock ones that you need to hear up to remove. The issue I'm having, how the heck do I put the rear u joint back on the axle. It's should be so easy but for me it's not. First the guy at the parts store gave me two sets of the fronts. I thought I got the correct rears but when I went for a drive the caps fell off, the clips dont hold them in. Any pressure and they just pop out, there isn't a channel for them to sit in. I am told my truck should be a stock drive line with a eaton posi. Good thing I have 4 wheel drive or I would still be on my back in the parts parking lot. Any help would be great, this is very frustrating.

[rjgti]

my 99 has small caps for driveshaft side and large caps for rear yoke

[txab]

Take the old joints with to get the correct replacement