1. I have contacted Belcom and they indicate that the BLT-8W BUC takes about 2 amps at 24V.https://www.belcommicrowaves.com/htmls/page_300.aspx?c0=179&bsp=54
Their spec sheet says 54 W. The iDirect 3000 uses an external power supply and I don't know what power supply that you have. Typically they are good for 5 amps at 24V. Check your power supply. Your power supply may be faulty and giving low voltage/current up the BUC cable. In which case the BUC will saturate at a lower power than its specification says.
2. Prodelin antennas have ABCD measurements which define the positions of the top and bottom of the feed window, relative to the top and bottom of the dish. Example:
This picture is an example only. It is a Prodelin Ku band 2.4m antenna. Note that your dish may have different F/D ratio (e.g. 0.8 instsead of 0.6 as in this example) and you are using a larger diameter C band feed. The focal point is some distance down inside the feed horn. In the above example A=55.5 inches. B=59.4 inches. The distance to the centre of the window is 57.45 inches and the focal length is 58.52 inches.
We really need to know the model number of your dish. Photos of the feed assembly would be helpful. Take a picture accurately from the side view.
3. NSS12 is circular polarisation at C band. There must be a long polariser tube (3) between the conical feed horn (1) and the OMT junction with waveguide (2).
Inside the polariser tube there will be rows of pins or slots. These pins or slots must be at 45 deg to the waveguide(s) to make circular polarisation. It is worth checking that you have a polariser and that it is aligned at 45 deg. The image above does not show the location of these pins/slots on the exterior of the tube. There are probably some tick marks on the flange like LHCP -45, Linear 0, and RHCP +45. Note that at the mid position, 0, when the pins/slots line up with the waveguide the effect of the polariser disappears and the feed becomes a linear polarisation system, which is not what you want.
If your OMT has an N type coax connector (as in the example image above) for the 6 GHz transmit connection then there is the possibility that the cable is faulty and has high attenuation due to moisture/water corrosion. The type of cable is typically Andrew LDF-450 Heliax. This type cable and the connectors are very expensive and take several hours skilled work to terminate!
Best regards, Eric