Gears not changing quickly enough. and then changing 10 to 15 seconds later after clicking shifter . when they eventually change they seem to thud down the cassette . no promblems putting them back up the...
Two things to this problem.
1. Clean your drivetrain REALLY, REALLY thoroughly with a good degreaser and a bristled brush. All of it. Clean the derailleurs, the chain, the cables. Once it is all cleaned up and dried off, lubricate the chain and the cables ONLY.
2. Shift your bike into the highest gear and release the cable. Pull it taut and re-tighten it. Flip it over and shift into your middle cassette cog while cranking the pedals. Use the barrel adjuster on your rear shifter to get the jockey wheel on the cassette aligned over the correct cog.
This was an abridged guide to rear derailleur adjustment because it sounds like it was more grunge in the cable or derailleur than anything else, but i'll check back and if this solution doesn't work out, i'll give you tips on a far more thorough overhaul. Just remember a clean drivetrain is a functional drivetrain, and the cables and chain are the only thing you are supposed to lube.
Hope this helps,