98 XLT Ranger 4x4 Transmission - Reverse

Just purchased a 98 Ford Ranger XLT with 52K miles. When shifting into reverse, it takes a good 3-4 seconds before the transmission drops into reverse. The dealer stated "no abnormal operation felt at this time, not fault codes present in computer". It's my son's first major purchase. I'm concerned as we only have a 30 day 2500 mile warranty. Any thoughts/commets? Thanks.