Hi guys,
Been driving this car for 3 summers now, but recently have been having a few issues.
Wondering if you guys have any experience with these symptoms.

Recently I have been having backfires when I let off the throttle, but power was still great.
In the last week, backfires have been getting worse.
Sometime in the last 2 months it developed a ticking sound at idle, but its getting louder. Sounds like a sticking valve, but I had the valves professionally done when I put the engine together.
Yesterday it ran really rough, it bogged badly when I stepped on the throttle . Power was way lower than normal so I drove it gently home.

At some time the engine check light came on.
By coincidence..... my speedometer started randomly fluctuating
When I checked the engine code with my ODB computer, I got P0500 - Vehicle speed Sensor A. Not sure what this means.

I am working my way through the engine and ECM, making sure all the connectors are secure and checking all my grounds first.
Then I am thinking it may be injector related. I'll pull each one out and see if it makes any difference.
Then I'll check the coils.

Not sure where to go after that.

Anyone got any ideas.... that would be helpful.