2005 Mazda b2300 transmission

Has the check engine light come on?

No the check engine has not come on at this time.

Since there is no check engine light, chances are all sensors and solenoids are working properly. That leaves the valve body in the transmission. Is the fluid clean?

Fluid has not been changed for some time, but it looks to be over full by the stick. Let me give you a little more background. A few weeks ago the oil cap was left off, over the next two days the truck was driven about 125 miles. Needless to say there was oil all over the motor. Up to this point the truck was running fine, after the oil went all over the motor we could smell a weird smell (this was when we found oil cap gone). The truck was not driven until there was a new cap, The oil and filter was changed. Once I drove it I could hear what sounded like a spark knock when driven normally and the transmission was not shifting correctly. If I start off slowly and pick up speed slowly it will shift fine but still hear a spark knock sound. I hope this Info may help you better understand what happened and what maybe my problem.
Thanks
C. Livingston

How low did the engine get on oil? Are you sure it's a spark knock and not a lifter issue?

Engine may have had 2 to 2 1/2 quarts of oil still in it was changed.