My '93 Saab has light brown foam in the top of the oil dipstick area. Light brown foam on the dipstick is never a good sign. You may be having crankshaft ventilation problem - check the breathers. In addition, check proper operation of the cooling system thermostat. Is the 7500-mile new rule for environmental purposes or can the oil withstand the pressures longer.
Synthetic oils do have a longer life than the petroleum based motor oils.
If you change your oil every 3000 miles, you probably will not get any benefit out of the higher priced synthetic oils. My truck used oil when new and continued to after I thought it should be broke in. I used it because they offer similar Cummins engines in their equipment. It seems to use less oil and the oil seems to stay clean looking longer. I have recently been told by people at Dodge not to use paraffin base oil in this motor.