Is it fire or fuel? I have no idea but the car will run great and then suddenly it will start jumping and jerking like a rodeo bull. Then just as quickly it will smooth out and run good again. It has 195,000 miles. I had timing belt done again in August 2010. A local garage checked the codes but they were 'dealer only'. Any suggestions as to what it could be or how I can narrow it down using troubleshooting techniques?

Are you using the same NGK platinum spark plugs that originally came in the SUV? Have they been changed in the last 40,000 miles or so?

Ethanol fuel related problem?

I would try to narrow down exact operating conditions to see what it takes to duplicate the misfire.
It could be something was on the MAF and caused erroneous data. A worn contact in the TPS can do similar things.
Do you plan to have the dealer check "their" codes? I would...