94 5.7 suburban code 32

I have a code 32 stored after the ‘service engine soon’ light came on briefly. This occurred after the following: a two hour highway drive at 65mph, an approximately 8 hour rest then about twenty minutes into the return trip the light came on for about five minutes and then went out. The exact same thing happened at the same place and time on the same trip just before Christmas. In that case the engine light did not come on again and the code disappeared after twenty? or so starts. My manual says this is EGR related otherwise truck runs beautifully. Suggestions?