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Replacement parts for WHIRLPOOL GR450LXHQ2 30`` ELECTRIC RANGE CERAN COOKTOP Convection Oven | AppliancePartsPros.com

Here is a service manual which may help but it does cover a number of units
https://secured.whirlpool.com/Service/SrvTechAdm.nsf/2cd44500d572193285256a45004fd9d6/5feedbe46138625985256aa1005ef62c/$FILE/8178042.pdf

Here is the tech sheet, see the attachment.

Sorry but I find your post a little confusing you say "oven that will not get
up to temperature" but then say "the bake element glows during preheat but does not come on after that" which sort of indicates that it does come out of preheat and therefore is reaching set point temperature.

There also seems to be a discrepancy in the manual where it talks about 2 sensors but the wiring diagram and parts only show one. This may just be because the manual is talking about another unit that is covered by it.

When the element do come on do they get a fairly consistent red in color?
Could be one of them is shorting through it's foot to the frame.

If the elements look OK then I would say that the control board is the cause of your problems.

The control board is Item 15 in Section 2 in the parts link.
The part number depends on the color.