I proudly own an 88 Chevy Silverado with a transmission problem . It has a 5.7L engine with an automatic 4 speed . I loaned it to local Shriners to sell watermelons from as a fundraiser . When number one son returned it it had reverse and first two speeds only . I dropped the pan and nothing fell out but fluid and filter dirty . Do I need a new transmission ? Truck has 147000 miles . Thanks in advance for any help .