1999 Burb bad fuel injectors?

1999 K2500 7.4L 454 144,000mi.
While on vacation pulling 6000lb travel trailer random misfire codes started appearing while climbing hills P0300 for 2,4,6&8 then P0175 neg fuel trim. MPG tanked and loss of power big time. (like pulling with brakes on, had to accelerate down hill!) Took it to dealer they diagnosed bad injectors.
#1 +7.8
#2 +3.1
#3 +4.5
#4 +2.3
#5 -1.6
#6 -6.4
#7 -3.7
#8 -3.6

Do they ALL need replaced? What should these #'s be if injectors were good?They quoted me $1344 parts only. $1754 installed w/ 1 year warranty . I found some bosh/ Ford motorsport with 3 year warranty for $309 for all 8.
Please advise.
Thanks

You could replace them your self for alot less. It is a fairly easy job. You have to pull the upper intake (8 bolts) and 3 bolts hod the fuel rail to the lower intake. You don't have to drain the coolant or pull the distributor. with hand tools it should only take 2-3 hours.

Did you replace the injectors??

I did replace them 2 weeks ago with the Bosch injectors, so far so good. I haven't run a whole tank through yet to compare mileage but it seems to run a whole lot better. Only time will tell on the longevity of the Bosch product. I am going to send away the stock ones to be cleaned & flow tested.
I'll post back any new information as it presents itself.

There has been some talk on other sites of using ford injectors on the 7.4 and I'm not sure how well it works

The Bosch are made by Ford Motorsport. The Ford logo is on the injectors.