These Tstats temp rating stamped on them are not always correct. I would put in 180 and see what happens. I have had the same problem as you with the temp getting up to 220 are so before the 195 stat opens enough to start cooling down to operating temp. A 180 will give you enough heat in the cab if you live in cold country. Double check your radiator cap that it is the right pressure.

Read your last post and had to add, they sell a dye you can put in the radiaor to see if you getting exhaust gasses in the coolant. I don't remember if you said you had the heads rebuilt and magnafluxed? I never had one that bubbled as long as you say yours has?