Intermittent & sudden loss of speedometer-91 Camry V6

My speedometer hardly ever works on my 91 Camry DX V6, but when it does it's for a short while. At low speeds seems to work up to 20-30 mph for a few to several seconds and then suddenly drops to 0 (zero). When I pull onto the nearest highway it will go up to about 70 mph over again a period of several seconds and then again nosedives to 0, then I go through a stretch of slower speed highway travel, about 1 mile, during which it still doesn't work (at 0), then I get on the Interstate, obviously higher speed, and it will work for several seconds again and climb again up to about 70 mph again and then suddenly drop to 0. Not totally sure but seems to start working again for few to several seconds immediately after slowing down and speeding up or stopping and starting. It doesn't bounce; it seems to work fine during those very very short stretches of time. After about 20 minutes or so; it seems to not work at all for the remainder of continuous travel.

I'm thinking speedo head, but am still in the dark. I replaced the VSS Vehicle Speed Sensor on the tranny/transaxle, but did not solve problem; seemed to register a higher speed though and work intermittently more frequently if that makes sense. Apparently It has both the speedo cable and speedo head sensor; I assume uses the LED, mirrors and light sensor setup in or around the speedo head, not positive.

I located a fairly cheap salvage instrument cluster; was thinking about giving it a try. Our mechanic said he'd have to drop the tranny and work on the guts of it for $750-$1000. Damn I hope it's just a sensor or cable, although again it's not jumping or bouncing; just smoothly goes up to a certain point and nosedives to 0.

Thanks for any and all help.

I posted this in Camry/Vista, but perhaps not the right place. This electronic/computer stuff gets a little hot to handle at times.

Keep troubleshooting sensors and wires. Sounds like a cold solder joint on the board or just a bad ground.