Why does my 93 ford diesel truck stall when letting off accelerator?it is 7.3 diesel engine and has a new injection pump.someone said something about a check valve?

The basic diesel engine troubleshooting link below may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-8.html#post1415281

General maintenance items, such as not changing air and fuel filters frequently enough, could be contributing factors. Ditto for oil level and changing engine oil and filter frequently, which affect fuel pressure.