1999 Jeep Laredo do we sell this car or repair?

Just replaced the transmission 2 months ago, the engice now clicks. Mechanic has checked for minor causes and says the cliicking is coming from deep in the engine - we have a bad engine. Estimate to replace enigine is $2,200.00. Mechanic's advice is to sell as is and not put any more money into car. Spent $2400 for rebuilt trnasmission. Car has 168,000 miles
Any thoughts? Thank you!