After I got a tune up at the local shop maybe a month ago my tuck has a knock when it is running and the idle is very heavy... I have even been asked if it was diesel just from the sounds... Also I have like another tapping from the engine that doesn't always happen but when I get to around 55 mph it will start

 

Change the fuel octane and see if that makes a difference.

 

Make sure they put enough oil in it.