Originally posted by StrechM
Engines generally last 5-7 gallons of fuel before showing serious signs of power loss. Of course it also depends on you driving habbits. The most important thing is proper care and maint., ie. clean filter, use after run oil, setting the piston at bottom dead center before the engine cools. Most of us have used the Sirio .18. It is a direct fit for the 2.5 and offers more pwer than the stock .15. I had good luck with both engines.
I forgot to mention that heat is a major issue on the 2.5, small displacement in a large truck. If you haven't already done so you may want to consider getting a temp gun.