2.8 turbo diesel Knock under load.

Just a quick one I have a 96 hilux with the above engine when towing my camper or loading up the engine up a hill etc it gets this knocking noise in it i have had the sump of plasti gauge the crank no problems and just for the hell of it with sump of i renewed big ends mains and the thrust washers and still have my noise to tight a to pay some one 70.00 phr to diagnose the problem any ideas of what to look for next would be appreciated. Thanks Gary.