He remained with the Rangers' organization until 1987 but was never able to completely get over the hump and earn a full-time roster spot, largely due to his being considered too small for an NHL forward.

Though initially spending time with Minnesota's farm team in Kalamazoo, Gagner broke out in 1989–90 with 40 goals and was in the NHL to stay.

Gagner, along with Ed Jovanovski, Mike Brown, Kevin Weekes and Florida's 1st round choice (Nathan Smith) in the 2000 NHL Entry Draft were dealt to Vancouver in exchange for superstar Pavel Bure, Bret Hedican, Brad Ference and Vancouver's 3rd round choice (Robert Fried) 2000 NHL Entry Draft.

In 2001, Brad Grant sold the Milton Icehawks to an Oakville trio that consisted of ex-NHLer Gagner, Mario Forgione who owned the Mississauga IceDogs at the time and was an automotive parts manufacturing president, and wine distillery consultant Ken Chase.

[4] Dave spent the 2006–07 and 2007–08 seasons with the Knights, and also opened a training centre in London to work with young prospects.