Hey,
my '98 f-150 STX has 98,000 on it. Bought it a few months ago. Changed oil once already because the dealer did not. It's time again and I am curious as to if I should switch it to synthetic. It doesn't leak any at all. Burns very very little if any at all. I do 90% in town driving. lots of stop and go.

 

This question has been asked many times already. The consensus answer is: YES

 

ok cool. I was looking at either Mobil 1 or valvoline Synthetic

 

City driving does impose a heavy demand on oil additive packages. They get consumed quite rapidly, so I can suggest going to a fleet service oil, Shell Rotella 5W40 full synthetic for example, and change at 5K intervals or more. An oil analysis at 5K will tell the story. Change intervals might go to 10K-15K depending on the results of an analysis. Of course similar results may be attained with a good grade of standard dino oil, but only with an analysis in there somewhere.