How do I find vacuum leak in 2002ranger3.0

Hello, Dave here, contributing to RepairPal and providing expert advice since 2010. What code is "saying vacuum leak"? I do not know off such codes. If you have engine "lean" codes, like P0171 and P0174, this indicates a possible vacuum leak, yes, but could also indicate a mass air flow sensor issue or air intake issue. Typically if you are trying to address and troubleshoot a vacuum leak, you would use something under the hood in the suspected areas of a leak to "richen" the air -- such as introducing propane. Propane in a vacuum leak area would quickly and briefly smooth out the idle. Since you are saying there is a loss oof power at 40 mph, I am concerned of an air intake restriction or an exhaust restriction more than a "vacuum leak". Hands on testing with an experienced technician is highly recommended. https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.