Rough idle

My 1993 toyota pickup 200,000 miles. My truck has been running very well, up until 2 months ago I had a complete engine tune up, oil change, oil filter, fuel filter, plugs, spark wires, cap and rotor, I had taken it in because my truck was running very rough at a stop the truck would "chug" when I turn on my lights it gets marginally worse. After the tune up my truck is still idling rough and has lost lots of power and gets horrible gas millage(about 6 months ago I was getting 36 mpg!) What is the problem? I was told by my Toyota certified mechanic that it could be valves? What is the cost for valves and your opinion on the truck? I know it has a lot of miles but its Toyota I want some life out of it!