1995 toyota 4runner sr5 v6 check engine light comes on when shifting auto transmission into overdrive

What is your question?

My 1995 Toyota 4runner sr5 3.0 liter v6 when the overdrive button is depressed on the automatic transmission shifting handle to shift into overdrive the check engine light will immediately or a short time after placed into overdrive. Just about the time I had first seen the CEL condition the speedometer stopped working( coincidence or not) ? Where or what can I do to further isolate this issue ?

What makes this problem better or worse?

No, it does'nt seem to matter if it's hot/cold

How long has your 1995 Toyota 4Runner had this problem?

I have seen this condition fo several months.