Will shift solenoid fix a slip between second and third gear

Hello, this is the Ford A4LD automatic transmission. The only shift solenoid in play here is the one that shifts from 3rd gear to overdrive. This transmission is largely hydraulically operated and minimally electronic. You also do have a torque converter solenoid. It is more likely that you have a mechanical concern, such as a modulator issue or a valve body issue. The good news: This is not that complex of a transmission and is not known for many catastrophic failures typically. The bad news: your vehicle is 25 years old and anything is possible. Ensure you have proper fluid level and clean fluid in your transmission. Beyond that you may need to obtain technical assistance.