I am confused about your actual dish configuration.
You say you have a D500 with an lnb added to it for 129 - I've NEVER heard of that configuration and if a Dish tech saw it he should know instinctively that it will not work because the 129 lnb is outside the focal point of the reflector.
You must have either a D1000, D1000.2, a D1000+ or a D1000.4WA already, or somebody did a major screw-up in installing your dish.
Assuming you have the correct dish (one of the 4 listed in the previous sentence), and still have very low signal on 129, you either need to switch to eastern arc with a D1000.4EA dish or add a wing dish specifically for 129.
If you do however still have a D500 Frankensteined by adding a lnb for 129, then you DEFINITELY do need to try a D1000.2 dish, because the D500 cannot see that added lnb, no wonder your 129 signal is so low.
All multiple lnb reflectors are designed to be slightly out of focus in the horizonal plane so those outer two lnbs get adequate signal, there is no boresight on multi-lnb reflectors, the pattern is an oval slightly more than 19 degrees wide and several degrees tall, not a round spot a couple of degrees in diameter.
Dish designed the D500, D1000, D1000.2, D1000.4, etc. all as compromises to get approximately the same signal, so just putting one lnb on one of these will get you nowhere.
You need to buy a single focus dish, probably a 24 or 30 inch reflector and mount your 129 lnb at the focal point of it and connect it either by a DPP44 or the auxillary input on the D500.
The obvious solution is to get the correct equipment, a D1000.2 for Western Arc or a D1000.4 for Eastern Arc, which you apparently do not have.
If you have Dish do your upgrade, they should install the proper equipment and make it work before they leave the scene of the crime.
If they do not, do not hesitate to make them come back and do it right.