If the dealer won’t lock you in on a value with your trade and the price on the ordered truck, you don’t want to be doing business with that dealer. Decreasing a previously agreed upon trade value or putting a surprise “market adjustment” on the deal when the new truck shows up is ultra scummy behavior on the dealers part.
Talk to the dealer you want to order from, ask them to value your trade, and agree that value will stay the same when your order arrives. They may not agree to it, nothing says they have to but a good, honest dealer will.
I ordered in March, truck arrived in June. My trade value was agreed to at the time of order. I put 7k miles on it between March and June, the amount they gave me did not change. The value was a touch lower than what I could have got if trading it in immediately to account for the additional age and miles. However, I think that’s a fair deal for both parties involved.
The new truck price was also locked in at time of order, I did not pay any of the MSRP increases that happened after my order was submitted.