No third in D but has it in OD 94 k1500

[S30love]

So I have had this truck since May of this year. It's 1994 ecsb k1500 heavy half, 35s and 410 regear. The truck has edlebrock tbi intake, and shorty headers. At some point it was someone's pride and joy. What I can't figure out is the transmission. No amount of research turns up any results for what I experience. No third gear access when shifter is in D, the 3rd selection from the right. In shifts 1-2 then holds 2 forever if you make it. Put the selector in OD and 3rd is there. 1-2-3-4. Torque converter lockup is there, the truck acts fine. Is it internal? Maybe neutral safety switch? Not realizing it's in D.... But 1 and 2 work fine. . . Fluid is red and smells fine. Pressures unknown. Just no 3rd in D. But has it in OD. Thanks for any ideas.