The first thing to check would be the condition of the clutch, if it is not releasing completely you will have trouble shifting into first since the engine is moving and the trans is not,all other gears when moving will be easier, next would be fluid level, then syncros.
A 1991 Toyota 4runner is bigger than a 1990 4runner
There is no recall for the Toyota 4runner transmission. Some Toyota's have had break problems that may have started the recall rumors on some Toyota products but, there is no recall for the Toyota 4runner transmission.
The 2012 Toyota 4Runner has 24 valves.
The 2012 Toyota 4Runner has a V6 engine.
The 2010 Toyota 4Runner has 16 valves.
The 2014 Toyota 4Runner has 24 valves.
The 2013 Toyota 4Runner has 24 valves.
The 2001 Toyota 4Runner has 24 valves.
The 2011 Toyota 4Runner has 24 valves.
The 2009 Toyota 4Runner has 24 valves.
The 2003 Toyota 4Runner has a V6 engine.
The 2005 Toyota 4Runner has a V6 engine.