Severe pull when braking???

1999 Tahoe 2WD 5.7 LT. I just developed this problem, when pushing the brake at say above 40 mph I will get a severe right pull to the point the ABS will engauge (sometimes). Here is what I have replaced so far. Installed two new calipers, both front hose brake lines. The pads are all good (used still) all the way around the vehicle. The rotors are also in good shape (used). Both lines have been bleed and are free of air.
I have inspected suspension issues and nothing is standing out as a problem. I just had it aligned and still no luck. I am going to look a little closer at possible worn ball joints, control arms and etc. But I really don't think there is a problem with any of these as handling is fine.
I was reading about the ABS sensors or even perhaps a micro-valve could I possibly have a problem with one of these?
Thanks in advance here for any help. I really want to get this problem fixed before snow flies!!!

Arty

Checking the front end componants is a good idea, But from what you are describing, I would lean towards a brake system problem.
Even though the rotors are used, are they above min thickness?
Are the nuts for the wheel bearings torqued properly?
I would check brake system pressure to see if it is equal between sides (you can buy the pressure guages from Harbor freight).

Thx for the reply GMMerlin. I have finished checking all the front end components and everything is in order. I just ordered a set of rototech drilled and slotted front rotors and I will be also installing new pads with those next week. I did a complete system brake line bleed today also for all four wheels using the proper order. I did have a small amount of air in one rear line and some blackened fluid. All said and done and no difference with the pulling issue. Tomorrow or Friday I am going to check fluid pressures on both front lines and I do have the pressure gauge but thank you for that additional help.
I also wanted to add that I am not getting any ABS codes from that system. I have on the other hand, been having the right front tire wanting to lock up and then the ABS ingauges more offen probably due to rainy weather here.

Also I will be checking those wheel bearing nuts... thx

bump....

For those of you that are interested. The answer to my problem ended up being a warped rotor. After replacing the rotors and pads my problem disappeared.
Additionally, I installed drilled and slotted front rotors (rototech brand not praises)and I also purchased a pad/shoe and spring kit from Praised and was nothing short of amazed at the braking improvement.

a warped rotor will not cause a pull, i have fixed several by swapping the front pads side to side, if this fixed it then i sold new front pads, contamination of lining by who knows what, also a good thing to check is caliper to knuckle clearance, .024 max combined top and bottom, if necessary you can file the knuckle.

So your thinking then is that the pads were the cause then. Because the problem is now fixed. Also would you define knuckle for me and thx for your help...

yes the pads were your cause. the knuckle to caliper clearance is measured between the ends of the calipers, you will have a small gap on the top and bottom to allow the caliper to float, if the clearance is to small then brake pull, uneven pad wear can occur. its the space between the steering knuckle and brake caliper.