What you are discribing is a lack of refrigeration capacity. What causes that?
Does the unit have enough clearances from other objects and heat sources.? Is it clear more than 6 inches to the rear? Room below 90F
Is the air filter clean? Remove and inspect with a light.
Is the condenser coil clean and clear? Again, a light shining through is the best check.
Is the condenser fan running at speed? Fan blade correct? Moving adequate air? This one is a common problem.
Last, is it fully charged? Does it have the correct refrigerant? If it has had work on it, did they replace the filter/dryer? For this one you need a licensed refrigeration tech. Find one that knows what he is doing. Ask your local RSES chapter for referrals.
Compressor amp readings directly correlate to load. Taken in with air temp measurements , one can tell it it has a cooling problem or capacity problem. How hot is the air from the condenser?