NOYAFA NF-8209S Network Cable Tester, Ethernet Cable Tester with CAT5, CAT6 Line Tracer, PoE, NCV, Length Test, Port Flashing, Fault Line Scan for Cable Grooming, LAN Network Cable Tracer Kit

100mbps isn't a symptom of improperly-grounded shielding. You have an open conductor or short between two conductors, probably on the blue or brown (using 568B sequencing) pairs, most likely on pin 8 (solid brown). From your description, it sounds like you bought a 150ft patch cable and cut in half then re-terminated. What AWG wiring was used in the patch cable? If it was smaller than 23AWG, the conductors might not be wide enough for the connector contacts to reliable pierce into the conductor. Note that larger AWG numbers result in thinner diameter conductors. It's also possible that a mismatch between the crimp die and connector could result in poor crimps. I currently use the Ideal FT45 crimper (as part of this kit) and also own the Klein VDV226-110, which are both great, (but don't do a lot of shielded cable runs). A network cable tester such as the Noyafa NF-8209S or Klein Scout Pro 3 would help you identify the problem. Both have TDR function that can show the distance to the fault (though Noyafa's is easier to use). Noyafa adds a crimp QC test to show if all the pins on a connector are making contact with the conductors.