You said a drilled well. So I assume it is cased all the way to the bedrock and has concrete grout from 20 feet below the surface up to the surface with a slab at the surface. I would try to shock it again. I like to use "Super Shock It" a granular chlorine. It is HTH chlorine and you can get it in a pool supply or some other stores that have pool supplies. Dump the HTH in and hook up a hose . Fix the hose so it goes in the top of the well and water runs down the inside of the casing . Allow the water to circulate. When it is mixed up good turn on each faucet in the house till you smell the chlorine then shut the faucet off. Flush all toilets, run showers the washing machine etc to get chlorine in all the pipes. The longer you do it the better. Circulate the water in the well for at least several hours and leave the chlorine in there for at least 24 hours.
Also your test results are so different. How were the samples taken? At the same time of day? Is there a reason for this difference that you know? Where was the sampling point? What type of faucet? Was one sample a first draw, this would be to let the water set all night and take a sample first thing in the morning?
Personally I like UV for disinfection and it would be after the iron filter. If iron is considered to be a problem you want to remove it so it does not coat the quartz sleeve in the UV light that could cause it to be ineffective. Also UV light bulbs have to be changed every year and cost about $80.00