The G05 (yellow) coolant is the same as the Ford Premium Gold. It is an extended life coolant that Ford began using about the time your truck was made, but then changed back to the traditional green coolant because, I think, the G05 is more expensive and they're trying to cut costs. Supposedly the green is compatible with the yellow, but if you change, I would recommend a good flush and staying exclusively with the yellow.

My 2001 came with the green, but I changed the coolant to G05 early on when I installed a coolant heater. I believe it is easier on the water pump and, of course, lasts longer. I do not plan to go the full 100K claimed life, however.

If your coolant level is not going down and your oil looks normal, you don't have a leak. The pressure cap is there to raise the boiling point above 212. If you don't get close to that, I don't think the pressure will rise.