I just changed the oil, filter, and air filter on my 3.7L V6 and now the check engine light is on and the truck won't go into gear. What could be wrong?

change the fuel filter and check the fuel pressure

Can't give you an exact number but I can tell you how to find out. I will asume that you are changing you oil and filter? After putting the oil plug and filter on put three quarts of oil in and start engine; after oil light goes off, turn engine off and let set for about 5 minutes, then check oil; if it is not on the low mark of dip stick add another quart, start engine, stop engine, let set for a couple of minutes and check again. By now you should either be at or above the low line and just add enough oil to top it off at the full line. I would guess that about 4 1/2 to 5 quarts is what you will need. Hope this helps,
P. Ford

YES CHANGE THE OIL AND FILTER SOON OR YOU MAY HAVE TO CHANGE YOUR ENGINE

no ,they very rarely need changing unless the metal canister has corroded ,most likely its a mass air flow sensor in the air intake pipe

Check oil sending unit.

i whould change the sensor thats most likely the problem

I had a similar issue on a grand cherokee '98 4.0L, and it was because the gearbox was overheating due to old oil and the fact that is was low on oil. Change gearbox oil and the filter inside the gearbox checked the two band tension and adjusted them and all was ok. the oil should be red or a dark pink. It would point more to this being the poblem if when it does change gear, the gear changes seam slow or slugish or change happens at higher engine revs. You may be able to get a fault code from ecu, by turning ign. to acc then on then off then on then off then on then off then off hen on again (code is displayed instead of odomitor reading as PXXXX or POXXXX). This could point you i one or more directions if oil seem to be correct.

how about ck,,coil,pick up coil, or modular,to see if u have an off voltage going to spark plugs

That car should use 5W30 oil, check on the filler cap, or owners manual. If you are in freezing weather, use a synthetic oil. The Change oil light is reset by turning the key on, then depressing the gas pedal to the floor 3 times. The Check Engine light is another subject and a repair shop will need to diagnose and recommend repairs. If it has a 3.0 V6 its not that user friendly. the Cadillac Catera uses that engine.

good chance with that problem you were close most likely a misfire will cause that. it would be either your spark plugs or coil pack. also make sure your vacuum lines are good and air filter is good. also bad gas can cause that problem. the worst outcome would be your throttle body going out on you.