LW300 tapping noise

got an 02 LW300 the other week, and was leaking oil. Took it to a local GM dealer, and had them look at it. They said it looked like the valve covers (this is the 3.0)

Yesterday, we did the valve (camshaft) covers. Real PITA job that was. Took it for a test drive afterwards, was running great... for hte first 5-6 miles. Then coming off the interstate, and slowing down, suddenly a lot of noise, loud tapping noise. Did we miss something, get something wrong? It sounds like an old Lumina (91 w/ 3.1 v6) we had, after it stopped getting lubricant to the rear cam, after a bit, that camshaft broke.

Any thoughts on problem?

Heres some videos with the sound

http://www.youtube.com/watch?v=02mv48RR6gU

http://www.youtube.com/watch?v=QAmtHJSfk0c

solid or hydraulic lifters? also check the oil level.