Is it a hydralic floor or cylinder jack?  When is the last time you
checked the fluid level in the jack?  I know when my 3 ton got low
once, it was a pain in the a.s to use.

Your registration isn't going to tell you how much the truck wieghs. I have
a 2500 quad cab 4X4 with the (heavy) diesel engine and it weighs less than
7,000 lbs empty. Maybe your jack is reaching the end of it's range of
travel. The 2 ton capacity should be plenty to lift a wheel off the ground.
Will a 2 ton jack safely hold the load? No. The jack is for lifting, not
holding. Get jack-stands to hold the load. I refuse to go under any vehicle
that's held up by a hydraulic jack.

Generally you want a Jack that has to use less than 50% of its rated
capacity to jack with. There is about 4000 lb of weight on your front
axle and when you jack it out inboard of the wheel you are actually
lifting more than half the weight on the axle and a 2 ton jack will
work pretty hard on such a load as will be seen by the effort required
to use it. I suggest a 3 ton bottle jack here minimum as it will
reduce effort to raise it and it will have a bigger base and more
saftey reserve capacity. The lowest capacity jack I have here is a 2
3/4 ton floor jack and I have a 3  and 5 ton bottle jack too. The 5
ton is about 20 years old now too and never break a sweat with any 4x4
or trailer axle I jack up with it.  
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