After runing for 5 min it starts making a dieseling sound, like lifters. At first only after puting under load, in gear. The noise increases as engine rpm's speed up. It runs great without anyother problems.

are you sure it's inside the engine? i've heard many water pump bearings on 3.8s be mistaken for engine noises.

if you want to try and pinpoint the noise, take a long (atleast 24")prybar/crowbar/screwdriver or anything else metal and touch it to a part of the motor and then put your ear to the other end. You should be able to pinpoint where the noise is loudest and come up with a reasonable solution.

Yes I believe it isn't the water pump, I replaced it about four months ago. I tried what you said about puting a dowl to my ear and sounding out the engine and can't locate it. The lifters are in the center. Thank you for your conern.

If it's not the water pump making the noise, and you're sure it's coming from the valve train itself, try taking off one of the valve covers, and make sure you have lubrication coming out of the push rods. if you don't have any oil in the upper portion of your valve train (and yes it's going to be messy so have oil dry ready), you can have a few problems on your hands. You can have a bad oil pump, which won't push the oil through the passages... You will definately have to replace the push rods, rocker arms, and maybe the lifters, depending if they have lubrication or not, and also depending on if they're mechanical or hydraulic. But definately check to see if you have oil coming out of the middle of the push rods. You'll see it flowing down them while it runs.