2010 Prius getting 40-42 mpg

No you're in the hills so that's probably going to be about normal My Gen 2 would get about 43 and a half miles per gallon there in the hills that is. And sunny North Carolina Central North Carolina mostly the flatlands I get about 46 47 maybe this is in my generation too My wife and a 13 persona and get about 46 to 48 has a heavy foot. Other people are going to say the car should get 50 miles to the gallon If I got 50 mi to the gallon in my 13 persona I would probably have a line of traffic behind me going to the state line or some such kind of nonsense never seen it And I've had good running Gen 3 and a failed engine generation 3 I've driven them in both conditions The Gen 3 even with a bad HV battery still most of the time stayed above 40 In real world mileage Toyota rated the car from 37 to well you tell me whatever it was

 

Try again. You can take it off (it’s a nut btw) any time, and leave it off. Ditto for the stud it screws onto (requires Torx E8 socket). This can be done at any time, without any other intervention, and left off permanently. See first two links in my signature. On a phone, turn it landscape to see signatures.

Did you note codes, and could you share?

 

Sounds like the brakes are seized up if the squealing steering went away. The hub slight movement allowing the rotor and pads to move while the caliper is more or less locked in one position one one side or both sides They seize up faster when they sit without driving. Try doing the 4 corner dissassembly/clean/relube of the sliding pins. You will probably need the grommet and dust boot kit and sliding pins so get it before you start.
The egr cooler cleaning won't boost your gas mileage much if any, but it makes the car a lot smoother at ultra low rpms. The big thing outside of that is make sure you did a great job doing that intake manifold clean. The car can't tell if it has good even flow to each cylinder after the valve so thats what kills them. Judging by that cylinder 1 misfire you did a good job catching it because thats the "death cel"
Do all of the maintenance you mentioned above as well and make sure you use pink coolant not red.

 

With p0301 (misfire on cyl 1), your miles , neglected EGR cleaning and symptoms, I’d focus on head gasket: they reliably start leaking coolant into cyl 1, around your miles and condition. Typically the wall between between cyl 1 and 2.

leak down test and boroscope inspection (with coolant system pressurized) are the usual diagnostic methods.

 

Yeah verify the head gasket is intact with a leak down test or a block test or both.

 

if you're going to do the head gasket, do it right, or replace the whole engine.

you can continue to drive, but keep an eye on coolant and oil levels

 

Once this is happened your engine is probably starting to buckle up squeeze in and suck in its butt cheeks whatever you want to say. So do the smart thing and just replace the engine from a low mileage takeout from the Japan domestic market It's the cheapest thing you're going to be able to do unless you have a friend or family in the business and can really do something for a less I doubt it Friends people will come out of the woodwork thinking whatever they think and then when they do their research they realize oh God so there you go You can fiddle fart around and have people doing their best work but if they're doing their best work on compromised pieces of metal then they're best work doesn't matter this is the problem You can be the best in the world at something but if you can't get the best things to work with well your work is not going to shine probably

 

If you can verify the head gasket is blown I wouldn't drive it. The start up knocks can get pretty violent which will ruin the engine. The head gasket replacement by itself is a lot easier.

 

Actually to be honest about it it's a lot easier to change the engine You think changing the head gasket and timing. Over and all that tight space business no it's much quicker to yank the engine out drop another one in spend the 4 hours bolting it up doing any housekeeping and whatever you need to do Way quicker at least it is to me