An estimate I sent to the Feds in early January never cleared my bank. Should I be concerned or are they backed up this far?

It is possible the IRS never received the payment or if they did it was not processed by the IRS.

Check your tax account to see if there is a payment recorded in January - https://www.irs.gov/payments/your-online-account

another way to pay is to use the IRS online resources to make tax payments. nothing gets lost in the mail. but correct info especially account and routing number must be entered or if you don't mind paying fees you can use a debit or credit card. most if not all states also have a way to pay electronically. 

at the end you get to print out a receipt should there be issues or use when entering tax payments in your return.

https://www.irs.gov/payments