1990 Toyota Pickup initial acceleration problem

Hi, I have a automatic 1990 toyota pickup. It has a 22RE engine and is a 4x4 with 193,000 miles. I've kept it in great shape but recently ran into an issue I can't figure out. Once 6 months ago, I pulled to a stop and started to accelerate again but the car was moving very slowly. It's similar to having your brake engaged when you step on the gas. I have to press down hard before it starts moving and then it's fine. This past week, the same thing occured again when I pulled to a stop light. It doesn't happen everytime though. I did notice that while I was trying to speed up, the O/D (overdrive) light flickered slowly a couple times. It stopped after everything was back to normal. I checked my engine and didn't see any leaks or anything abnormal. Any idea what the problem might be? Thanks.