19 is the most often used channel, truckers tend to run on it too. Proper etiquette, if you reach someone on 19, and want to carry on a conversation, both should switch to another channel so as not to tie up 19. It's ok for a quick back and forth, but if its going to be a long winded one, switch channels. 9 is for emergencies.
T/signal, most likely the switch is bad. Does it work if you put the 4 ways on?
If the left comes on but doesn't blink, then you have a bad flasher.
Stab will cover up but not fix the problem. It's usually the track bar bushings.
Track bar attaches to the right frame and front axle. If the bushing is worn it allows the axle to shift back and forth. Have someone turn the wheels back and forth as you watch the frame end of the bar. If you see it moving side to side it's bad.
You'll either need to replace the bushing or just replace the track bar. Also if it's lifted that much, the track bar is either relocated or replaced with an aftermarket unit normally.
Also check everything else under the front end for play. Ball joints, tie rods, pitman arm, drag link. And tire balance and irregular wear on the tires can aggravate the problem.