It may or may not be a horrible deal. My suggestion is, get the payment out of the picture. Here is the math you need:
Purchase Price of New Yukon = P
Trade in Value of your Taho = T
Payoff on 2021 Tahoe = Z
Dealer Fees = D
Taxes = t
Title, License, Transfer Fees = L
Your
Real Cost, C is defined by
C = P - (T - Z) + D + t + L
Then, since you are financing, you need to consider:
Annual Interest Rate converted to a decimal = r (ie: 4% = 0.04)
Number of months = n
Total Interest you will pay = I
For a 4 year loan, you can calculate the total interest you will pay from this formula:
I = C * [(1 + r/n)^n – 1]
Or an easier way is use an online loan calculator -->
https://www.calculator.net/auto-loan-calculator.html
Add I to C to see the real cost of the deal. If you want to see the delta cost between sticking w/ your current vehicle and now, you would need to determine the remaining interest you have to pay on the current vehicle...but, what is going to get you is that on a 4 year loan, about half of the total interest expense comes in the first year..so you are basically resetting into the high interest part of the loan, and I am almost positive that you will be paying a higher interest rate originating a loan now that you were in 2021.
One wild card could be that GM was offering 0% for 36 months...if you could sneak in to this financing, you would actually
save money on interest vs. what you were at.