It sounds to me, despite your stove
being relatively new, that you have a somewhat clogged orifice in your oven
burner. The symptom you describe will typically result in the burner producing a smaller than normal flame. Compare the flame on one of your stove
top burners (same size; 5000 BTU most likely) with the one in your oven
, removing the bottom pan if you need a clear view of the burner, as a low flame is about the only way you can fail to get 450 or so inside the oven.
Clogging can result from dirty propane (compressed using a leaky compressor wherein some of the lube oil gets into the gas) or perhaps you simply have some junk in the gas line
leading to that burner. A tiny scrab of teflon tape, if someone used that (which they shouldn''t have) when hooking up the stove.
To unclog (and mind you, this is against your owner''s manual instructions), take off the burner cap, remove the small phillips screw, then remove the small round shield that the screw held in place, and then orient a pair of needle nose pliers vefrtically, such that it can grip the brass orifice body in the middle of the burner base. Unscrew the orifice (I''m sure there''s a ''real'' tool to do this...), and then look thru the sewing kit to find a needle that isn''t bigger than the orifice but also isn''t smaller. Ram that back & forth in the orifice hole (sometimes gunk is visible on the needle when you do this; sometimes not) and then pin the needle onto one of the manual pages, so you''ll have it next time. (There will likely be a ''next time''). Before reinstalling, consider placing a vacuum hose over the burner, flush and with a good seal, and then turning on the vacuum and momentarily (one a few seconds!) opening the solemoid and then that burner. The idea is to allow any junk caught in that burner line
to be sucked into the vacuum, while being ''pushed'' by the low pressure air/propane.
Reinstall and compare the new flame with the old flame to see if you made a difference. If not, perhaps you didn''t use a big enough needle.