We have an old extended definition plasma at work with the lg panel and boards inside .Lately the picture has become jittery and jumpy horizontally.Looks just like a 60s set that needs its horizontal hold adjusted.
Any ideas what it could be?

Sounds like it could be a mainboard issue. Some of those smd caps going tits up. Try plugging the source into another input(if possible) and try that. Also see if it jitters when you are in menu mode. It could be lots of things but without seeing what it looks like it's just a wild guess.

I actually just rescued an EDTV Gateway plasma from the garbage a few weeks back, it was made by LG or at least used mostly LG components (and I fixed the supposedly unfixable Gateway plasma).

This probably is a mainboard issue based on my investigation of the set but could be bad caps as well.

Investigate that thing with a fine tooth comb. I found numerous bad caps in the Gateway. 3 main filter caps on the PS, one on an audio board, one on the X sustain (some sort of smaller cap domed really bad), blown module on the X sustain (probably from the bad cap). The odd thing was the caps appeared bubbled (aside from the metal topped small one) but it was really just the plastic (I peeled the jacket off), the inside looked good, but they tested bad. Samwha brand (supposedly their "good" series too). The sets run hot and obviously exposed to some heat.

Set I got looked like it hadn't been used in years, probably too expensive to fix or at least have someone do it. I spent like $40 getting it running. I bought some supposed Rubycon and Nippon Chemicon caps (cheapest possible, from China, probably fake) replaced all the offending parts. I plugged it in told my wife I was gonna fire it up and see what it was going to be, I told her to guess, pop and die or it would work. Well it worked. Been using it to play video games for a few weeks.

Not too terribly concerned about the longevity, there are so many caps potentially to go bad here I'd spend more replacing them all than the set is worth, it was more an exercise in if it could be fixed.

There were lots of rebranded LGs back then, or ones using LG components. I'd start looking for bad caps before doing anything else. If its the mainboard unless you find a cheapy used one its probably not worth replacing.