looking at a 99 6.5 td

[hatzie]

I concur. There is no way a mechanical lift pump problem would have allowed it to run better when it warms up.

The 1994-2001 DS4 6.5L uses an electric lift pump mounted on the frame under the driver seat. 
The lift pump might've been the only problem but I've seen similar operation with injection pump solenoid issues.  Properly rebuilt DS4 pumps are not cheap and they're a pain in the neck to replace.

The DS4 isn't oogy boogie or a dark art or whatever other comment that can be made about it.  They require a little more care than the old DB2 on the 93 & prior 6.5L & 6.2L engines.  Again the snake oil salesmen that tell you you need to relocate the PMD are full of it.  I've run five DS4 equipped trucks for over 300,000 miles without trouble from the PMD.  I did remove the PMD, dress the mounting pad so it was flat and smooth and re-install them with heatsink grease.

[82silverado]

The more I read, the more I learn something I did not know before. Good information on this site.

[Irish_Alley]

yea this truck had 200k on the stock location about the pmd box. ive worked on 2 other ones and ended up giving one away after we couldnt figure out what was wrong with it. the engine had a chance to warm up while we were driving it but not to OT.

[Irish_Alley]

or he could of been totally lying about it stopping once warm just to make the owner feel like it was an easy fix or they could just live with it