I just changed the oil and now it ant running write now when i step on the gas it does not move and i step harder and it clunks in and goes seems like a tranny ishue it was fine befoer the oil change

Take it to a qualified repair shop.

its not the worst thing you can do oil still protects motor ,I would change it AS/AP it can cause pump to work harder to move oil,and slow movement due to thickness. bad gas mileage could be air cleaner ,spark plugs,bad wires,motor running on the rich side

could be the head gasket has gone take out spark plugs and check there condition and look for water in the piston, water and fuel dont burn well. as you have done an oil change it may have gotten into the oil but its harder to tell with new oil, as water will sit on the top of the oil.

speed sensor??

never, I've seen them rust off. and there should be no reason to move it for a break service.

Sounds like you have a sticking valve. Drain about 1 quart from your oil. Pour a bottle of engine cleaner into the oil. Let the engine run for about 5 minutes, turn engine off and let the oil drain back down, give the oil time to cool. Drain your engine oil and replace the oil filter and new oil. Sometimes this will have to be done 2 times. But I would do this once and then do this again in 500-1000 miles. the reason you hear the noise go away is, the engine reaches a higher rpm the vales are working faster and harder preventing it from sticking.

Most likely the fuel pump is failing, the fuel pressure check valve is defective and the system loses pressure the long crank is due to this loss of fuel system pressure.

\'93 Hyundai Lantra, automatic transmission has trouble changing up from 1st to 2nd, it tends to rev on a bit, clunks once or twice before changing to 2nd, other gears seem to be ok. Oil levels are ok and have recently replaced the transmission oil (yes the correct oil was used)

you need to change the oil thre times every 3000 miles and youll feel the difference. It happens because you take a long time to change the oil and it creates oil clots and it is harder for the pistons to move

it sounds like your oil pump or your oil pick up might be blocked.
Try running an engine oil flush and changing your oil