I have an old Delta 14" saw that I have had for probably 15 years or so and works very well for most anything I find a need for with the right blade. I have found that with any tool they all need a little tweaking to perform to their full potential.
One thing to check first is to make sure the wheels are co-planar, turning in the same vertical plane, might need to bush one or the other to achieve this.
Good guides are essential- i replaced the steel ones with the poor mans fix- graphite ones and make sure your thrust bearings are up to the job.
Check the tyres, i turned the ones on mine on the wheels to true them to center, just needed a little on the high spots.
I replaced the drive belt with link belt, made a lot of difference with smoothness and vibration.
Buy quality blades for the right job and play with the tensioning, just becase the guide says its correct for the size blade you use doesnt mean it is . You will just have to experiment to find the sweet spot for the blade you use. I am usually tensioning more that the notated guide amount, but then again my saw is old and the springs might have lost a bit.
Its a little aggrevation to do all this at the beginning , but in the long run it will pay off in a better running machine.
Jerry Fisher