hi again, i have had a clunking noise while the engine is running at about 25mph or less, otherwise it goes away. Now let me start by telling you what i have found, first a leaking crankshaft seal, this i will replace. i have used a dowel and checked all the compoinents, like alternator, air cond. unit.. to find the clunking noise. I thought it was a flywheel cracked or warped, nope it was fine. when we rebuilt this 4.3 it was bored out 40 thousands over, a standard oil pump was used, i have a high efficentcy pump with a steel arm. they said the standard has a nylon one. i was also told that perhaps it was low on oil and may have damaged the bearing in the front. either way you cant miss me comming down the road under 25mph, makes a loud boomp boomp boomp noise, hmmmmm hope the crank isnt damaged, also the oil pressure guage starts up in the high side but after running for 10 minutes it will drop to half and then when you come up to a stop it drops in the red, you have to rev the engine up a little to get it to the first square, well any input will be appreciated