This is not true.
The truth of the matter is that synthetic oil will out perform conventional oil in all conditions, but especially in stop and go traffic. Viscosity break down is one of the main determining factors in the service life of the oil and directly effects how well an oil protects. Conventional and synthetic have different service recommendations for extreme operating conditions verses normal operating conditions. The thing to remember is that most people think that just driving slow and easy is normal service, but stop and go traffic on hot or cold is actually more extreme than say highway driving. Because of this, the most extreme conditions, besides an extremely heavy foot and racing, is when you only commute maybe 20 miles or less in stop and go traffic. A person who commutes 30, 40, 50 or more miles daily, and does so at a steady pace where it isn't stop and go is going to be closer to normal.
That being said. a conventional oil designed to go 3-7K miles is not going to be able to protect as well as an oil designed for extended intervals. The reason is actually quite simple, on a molecular level, conventional oils have all different sized molecules. Some that are let's say small like this . and some that are larger like this 0 . When the oil is flowing through the hot engine, the larger particles move slower than the smaller particles and as a result they tend to accumulate at the sides of the galley walls and wind up "burning up" creating sludge. The smaller molecules flow through the center of the flow moving faster. Well, one of the jobs of the oil is to assist in carrying heat from the engine to the oil pan to be cooled by the flow of air across the pan. But if the oil is flowing at minimal pressure with no air flow in stop and go traffic on a hot day, etc. The burning "effect" is going to be exagurated. This will also make the cooling system work harder because the flow of air into and across the engine isn't there from moving down the road. Thus, you wind up with oil that is quickly breaking down and losing it's ability to protect your engine.
Synthetic oil molecules are uniform in size and flow evenly through the engine. This results in more of the molecules being able to make contact with the galley walls helping to carry the heat into the oil pan. While also not getting "burned" along the sides of the galleys causing sludge. Because they are designed to maintain their viscosity longer, they do not break down as quickly as conventional resulting in better overall protection for your engine.
Synthetic will cost you more to purchase, but in most cases regardless of brand, you have the ability to extend service intervals while providing superior protection. However, no matter what oil you plan to run in your truck, make sure that you follow the service interval recommendations of the oil manufacturer.
