Having a slight issue with my truck. Under heavy acceleration I'm getting the pinging issues. Several times I've used 93 octane but it's has not changed the pinging. I also get the rattle when climbing steep terrain. I'm thinking the chain may be getting a little too worn. Truck runs fantastic but has over 300K on her, around town and 90% of the time highway it's normal till it downshifts into a lower gear for hills or passing. If you ease into it, it accelerates normal. I have used Sea Foam and also pulled the plugs and put trans fluid in each cylinder once to help clean out any carbon deposits. Time for a chain or some other timing issue? It's a 4.0 OHV. Thanks in advance.